+860diagnostic pages

3languages · fr en it

100%free, no sign-up

your bikehas aproblem?

describe what you notice — smoke, noise, power loss — and trace it back to the cause, test by test.

start a diagnosis explore the parts

+860diagnostic pages

3languages · fr en it

100%free, no sign-up

Why this site

Understand your bike — no jargon, no stress.

Many riders give up on understanding a fault for fear of making it worse, or pay a lot for a diagnosis they could have approached themselves. MotoDiagnostic starts from a symptom you can observe — smoke, a noise, a power loss — and guides you, test by test, to the most likely cause and then a clear course of action.

Our mission and method

“If you're not sure, stop everything. Better to spend 30 € on a diagnosis than 300 € on damage.”
Freeno sign-up
Guidedtest by test
Carefulsafety first

What symptom are you noticing?

Choose the sign that best matches what you see on your motorcycle. If several symptoms occur together, start with the one that worries you most or appeared first: we then cross-reference your answers to narrow down the most likely cause.

Blue smoke from the exhaustBluish smoke — sometimes gray and a bit oily — comes out of the exhaust. In almost every case, this means a small amount of engine oil has gotten into the combustion chamber and is burning along with the fuel mixture: oil produces this characteristic blue tint, while excess fuel would give you black smoke, and coolant would give you white. Telling your engine type apart matters a lot here. On a two-stroke, oil is deliberately mixed with the fuel (manual mix) or metered by a pump (separate lubrication) to lubricate the bottom end: a light haze of blue smoke, especially when cold or when you roll on the throttle, is completely normal and nothing to worry about. On a four-stroke, oil and fuel are entirely separate systems: any persistent blue smoke is abnormal and points to internal wear. Signs that go along with real oil consumption: the level dropping between oil changes, an acrid, oily smell at the exhaust, a black and wet spark plug electrode, oily deposits inside the muffler. On a 4-stroke, when the smoke shows up strongly points the diagnosis in a direction: if it only appears at startup and then clears once the engine is warm, it's usually the valve stem seals; if it's there all the time and gets worse under acceleration or when you back off the throttle after a long downhill, it's more likely the piston rings. Urgency threshold: as long as you keep an eye on the oil level and top it up, you can keep riding, but consumption above roughly 0.5 L per 1,000 km calls for a prompt engine diagnosis to avoid fouling the catalytic converter and, eventually, engine damage.Diagnosis available

Black smoke from the exhaustBlack, dry, thick smoke that smells strongly of unburned fuel comes out of the exhaust. It almost always means the same thing: the engine is getting too much fuel relative to air, the mixture is 'too rich,' and the excess fuel doesn't fully burn — it comes out as black soot. This is the exact opposite of blue smoke (oil) or white smoke (water or coolant). Whether your bike has a carburetor or fuel injection matters a lot for this diagnosis. On a carbureted bike, richness comes from a choke left on, a clogged air filter, a float bowl level that's too high (float or needle valve), or jets sized wrong. On a fuel-injected bike, it's a sensor lying to the ECU (engine temperature sensor, intake air pressure sensor, oxygen/lambda sensor) that pushes it to inject too much fuel. On a 2-stroke, slightly oilier, bluish smoke can mix in with the black due to the premix oil. Accompanying signs: a strong smell of fuel, a black and dry sooty spark plug, hard hot starts, an unstable idle, higher fuel consumption, power loss, and sometimes popping on deceleration. Urgency threshold: running rich for a long time isn't harmless — the excess fuel washes the oil film off the cylinder walls (premature wear), dilutes the engine oil in the sump on a 4-stroke, fouls the spark plug, and can destroy the catalytic converter through overheating. Always start with the free, trivial causes — choke and filter — before considering a carburetion adjustment or an electronic diagnosis.Diagnosis available

White smoke from the exhaustWhite smoke comes out of the exhaust. The good news first: in the vast majority of cases, especially in cold or humid weather and only during the first few minutes, this is simply condensation — water vapor that naturally forms in the cold exhaust and evaporates as soon as the pipe warms up. This is completely normal and needs no repair. You tell them apart on three criteria: persistence, smell, and fluid levels. White smoke that disappears after two to five minutes once the engine is warm is harmless. On the other hand, dense white smoke that persists when hot, that smells slightly sweet or cloying (the characteristic smell of the glycol in coolant), accompanied by a coolant level that drops with no visible ground leak, signals a serious problem: coolant is getting into the combustion chamber and burning there. The most feared cause is a failing head gasket, occasionally a cracked head or a base gasket. An additional clue to check under the oil filler cap and on the dipstick: a beige "mayonnaise" emulsion signals a water-oil mix, an almost certain sign of a head gasket. More rarely, water or condensation in the fuel produces whitish smoke with misfiring. This symptom mainly concerns liquid-cooled four-stroke engines. Urgency threshold: if the white smoke persists when hot and the fluid level drops, stop riding — an engine drawing in its coolant can seize or suffer hydraulic lock, damage far more costly than the diagnosis.Diagnosis available

'Clunk' / rattling noiseA repeated metallic noise, a 'clack clack' or clicking sound, shows up while riding or accelerating. The key question that guides the whole diagnosis is where the noise is coming from: the engine (up top, around the cylinder head) or the drivetrain (chain, rear end)? A simple test settles it: if the noise follows engine revs (it speeds up when you give it gas, even standing still), it's coming from the engine; if it follows rear-wheel speed (it slows down when you pull in the clutch while riding), it's coming from the drivetrain or a wheel bearing. The most common and simplest causes are mechanical and easy to reach: a loose or worn drive chain that clacks (cause number one, and adjusting it is a basic skill worth knowing). On the engine side (4-stroke), too much valve clearance makes a regular clicking sound 'up top,' more noticeable cold and easing off as it warms up. More serious, a worn cam chain tensioner or cam chain makes a metallic noise that follows engine revs and doesn't ease off: this is expert-level work, since a skipped cam timing can wreck the engine. Finally, a worn bearing (wheel or crankshaft) causes a dull noise or abnormal play. Urgency: a clacking chain can be adjusted calmly, but a clear timing-chain noise or a wheel bearing that's grinding call for prompt attention — a skipped cam chain or a failing wheel bearing are serious. If in doubt about whether it's the engine, get it checked quickly.Diagnosis available

The bike won't startYou press the starter button and the bike refuses to start — either it stays completely silent, the starter spins without the engine catching, or you just hear a single 'click.' In nearly every case, the cause falls into one of four families: a safety interlock out of position (kill switch, side stand, neutral), a dead battery, running out of fuel, or a spark plug that's no longer sparking. More rarely, it's the starter motor itself or its relay, but that accounts for less than 10% of cases according to specialist shops. Before any costly work, follow the diagnosis in the order given: you'll rule out the free, trivial causes first, and only need to get your hands dirty as a last resort. If the bike has been sitting unused for several weeks, the battery is statistically the first thing to check — it can lose up to 1% of its charge per day at rest. If you just ran out of fuel and refilled, the plug may have flooded after a few repeated attempts.Diagnosis available

Jerking / hesitation under accelerationThe bike bogs down, coughs, hesitates, or misfires as you accelerate: the rise in revs isn't smooth and consistent. The engine isn't getting its fuel or spark right when you open the throttle, and the approach is to isolate where things are getting stuck — fuel supply, ignition, intake, or electronics. The carburetor/injection distinction comes first, since it rules out certain causes right away. On a carburetor, jerky acceleration often comes from partially clogged jets (flat spots on acceleration, sluggish pickup) or from stale fuel/water in the tank (misfires). On the ignition side (applies to both types), a worn spark plug or a damaged lead/cap lets the spark fire intermittently, especially under load at high revs. A parasitic air leak in the intake leans out the mixture and creates jerkiness, especially at low revs and small throttle openings. On a fuel-injected bike, a dirty sensor or injector causes jerkiness, sometimes with the check-engine light on. The distinction sharpens based on the rev range where it happens (low revs = air leak/carburetion; high revs/load = ignition), how old the fuel is, and whether the warning light is on. Urgency: jerky acceleration isn't dangerous in itself, but it ruins the fun, can catch you off guard (a jerk mid-corner), and signals an engine that isn't running right — worth diagnosing, starting with the simple, free causes (fresh fuel, spark plug, checking for air leaks) before pulling the carburetor apart or plugging in a diagnostic tool.Diagnosis available

The battery keeps going flatYou have to recharge the battery regularly, the bike is hard to start after a night or a few days sitting, or you need to hook it up to a charger to get going. A battery that keeps draining has three main explanations, which you can tell apart with a simple approach: the battery itself is worn out and no longer holds a charge; the charging system (alternator and regulator) isn't recharging it while you ride; or a hidden draw (a current leak) is draining it while parked. On top of that, there's a harmless and common cause to rule out first because it's free: loose or corroded terminals that prevent proper charging. Two key observations help you tell them apart. First, age: past 3 to 4 years, a battery is statistically near the end of its life, making it the most likely cause. Second, when the draining happens: if the battery drains even while riding (it's not recharging), it's the charging system; if it drains mostly while parked overnight, it's a current leak or a worn battery. A multimeter is the go-to tool: it measures resting voltage (12.6-12.8V for a full battery), charging voltage with the engine running (roughly 13.5 to 14.8V expected), and leakage current with the ignition off. Urgency: no immediate danger, but a chronically drained battery sulfates and dies prematurely, and overcharging (above 15V) destroys the battery. Better to diagnose it early, always starting with the simplest and most common thing: the condition and tightness of the terminals, before suspecting the battery, the charging system, or a current leak.Diagnosis available

The engine stalls often while ridingThe bike shuts off on its own — at a stop, while decelerating, when you let off the throttle, or while riding with no obvious pattern. It's annoying and sometimes dangerous (stalling mid-maneuver, in a corner, or in traffic). The cause is most often related to fuel supply, idle adjustment, ignition, or electrics, and the approach is to look for what all the stalling situations have in common. Main causes: irregular fuel delivery (a blocked tank vent, a dirty fuel tap/filter, a pinched line — the engine is intermittently starved of fuel), an idle speed set too low (the engine stalls as soon as you let off the throttle or when stopped), a failing spark plug or plug cap (ignition cuts out intermittently, especially when hot), a loose electrical connection (a loose ground, damaged wiring, a temperamental kill switch that cuts the engine unpredictably), or, on fuel injection, a sensor that drops out (often with the check-engine light on). You can tell them apart by when it stalls (at a stop = idle; no clear pattern = electrical/fuel; when hot = ignition), whether the check-engine light is on, and how easily it restarts. Urgency: stalling can be dangerous depending on the situation (loss of control, being caught off guard in traffic) — diagnose it without too much delay. Start with the simple checks: idle speed, spark plug condition, tank venting, and grounds, before moving to electronic diagnosis. Recurring stalling always ends up having a logical cause you can pin down by noting the circumstances.Diagnosis available

Dimming headlights / charging problemThe headlight brightness varies with engine revs (dim at idle, brighter when you rev), the dashboard dims, accessories misbehave, or a battery warning light comes on. These signs indicate the charging circuit isn't doing its job properly anymore: it's no longer maintaining a stable voltage and isn't recharging the battery enough. The charging circuit includes the alternator (a magnet-carrying rotor driven by the engine and a wound stator that produces alternating current), the regulator/rectifier (which converts this to DC and caps the voltage around 14.5V), the wiring connecting them, and the battery, which buffers everything. Causes: a failed regulator/rectifier (unstable charging, pulsing headlight, or overcharging), a failing stator/alternator (not enough current being produced), corroded or melted charging-circuit wiring (which drops the charge — a common and inexpensive cause), or simply a battery at the end of its life (rule this out first). You tell them apart with a multimeter (measuring charging voltage with the engine running, roughly 13.5 to 14.8V expected, is the go-to method) and by observation (does the headlight follow engine revs? is a battery warning light on?). Urgency: no immediate danger, but a failing charging system will eventually drain the battery and leave you stranded; and conversely, overcharging (a failed regulator) 'cooks' the battery and can damage the electronics. Better to diagnose it early. Start with the simplest and cheapest things: the battery's condition and the charging-circuit wiring.Diagnosis available

Pinking / knocking noise under accelerationA thin, sharp metallic sound, like 'a handful of marbles shaken in a tin can,' shows up especially uphill, under full load, and mostly at low revs. This noise, called knocking (or 'pinging'), is a sign of pre-ignition: the air-fuel mixture is igniting on its own, too early, from the heat and pressure, instead of waiting for the spark plug's spark. These multiple flame fronts collide and create pressure waves that hammer the piston: that's the sound you're hearing. Knocking isn't trivial — sustained, it overheats and can damage the piston, rings, and cylinder head — hence the importance of fixing it promptly. Causes, from simplest to most technical: fuel with too low an octane rating for the engine (the most common and easiest to fix: just refill with the correct octane); a mixture that's too lean, which raises combustion temperature (carburetion, air leak); carbon deposits in the combustion chamber, which locally raise compression and create hot spots; and too much ignition advance (ignition out of adjustment or a faulty sensor), which triggers combustion too early. The distinction is useful: knocking that shows up right after a fill-up at an unfamiliar gas station points to the fuel. Urgency: don't let knocking linger — ease off (avoid heavy loads at low revs) and fix the cause quickly, starting with the simplest and free one: the fuel.Diagnosis available

It uses too much fuelYou're filling up much more often than before, your range has shrunk, or you're calculating a fuel consumption per 100 km well above the model's normal figure. Excessive fuel consumption almost always comes from a mixture that's too rich: the engine is getting too much fuel relative to air, and the excess fuel is wasted. Two mechanisms cause this richness: either there's not enough air (a clogged air filter choking the intake), or there's too much fuel (carburetion or fuel injection out of adjustment, jets too large, float level too high, a choke stuck on, a failed O2 sensor on fuel injection). A separate cause, not to be overlooked: a fuel leak, which lowers the level even without riding, with a characteristic smell and marks on the ground — needs urgent attention since it's a fire risk. Signs that go along with excess richness: black smoke from the exhaust, a strong fuel smell, a black and dry spark plug, fouling, sometimes a power loss. The approach is to rule out causes from simplest to most complex: start with the air filter (the most common and easiest) and the choke, before carburetion, and save electronic diagnosis (O2 sensor) for last. Urgency: excess consumption alone isn't dangerous, but it's costly and signals an engine that isn't running right (premature wear, fouling, a risk to the catalytic converter); and a fuel leak, on the other hand, calls for stopping immediately. Better to diagnose it early: the most common cause is free to fix.Diagnosis available

Hard to start when coldIn the morning or in cold weather, you have to crank it for a long time, hit the starter repeatedly, or use the choke several times before the engine catches; but once warm, everything's fine and it starts right up. This cold/hot contrast is very telling: it almost always points to an enrichment or ignition problem when cold, exactly when starting conditions are toughest. When cold, fuel vaporizes poorly, parts are at their widest clearances, and the battery delivers less current: the engine needs a richer mixture and a strong spark. The main causes are therefore: a cold-enrichment device (manual choke or automatic enrichener) that's stopped working, a slightly weak battery (cold reduces its capacity, and the starter struggles), a worn spark plug (that manages fine when hot but struggles cold), or a partially clogged idle circuit that starves the engine of fuel right at the critical moment of starting. Useful distinction: if the bike starts perfectly once warm, the problem is cold-related (enrichment, idle circuit); if it's hard when hot too, look toward the spark plug or battery. And depending on whether the starter cranks the engine vigorously or weakly: a weak starter points to the battery, a vigorous starter with an engine that won't catch points to enrichment or the spark plug. Urgency: no danger, but worsening cold starting often signals a battery or spark plug nearing the end of its life, best addressed before it fails completely.Diagnosis available

It starts then stalls immediatelyThe engine catches and runs for a second or two, then dies, and the pattern repeats on every attempt. This signature is very telling: the engine starts on the fuel already present in the carburetor's float bowl (or an injection priming charge), but something is preventing it from getting fuel or being allowed to keep running once that reserve is used up. So you're looking for what 'cuts it off' right after starting. The main leads center around fuel supply and safety systems. On the fuel side: clogged jets or a clogged idle circuit (the engine runs on the float bowl reserve then stalls from lack of continuous fuel supply), a dead vacuum-operated fuel tap (that no longer opens to let fuel through), a blocked tank vent (a vacuum builds up and cuts off fuel flow), or a mismanaged choke (left open, or not used when cold). On the electronic side, on newer bikes: an immobilizer/security system that doesn't recognize the key allows a brief start then cuts the ignition, with a key/lock warning light on. Two quick tests strongly guide the diagnosis: loosening the tank cap (if it no longer stalls, it's the vent) and holding a bit of throttle (if the engine keeps running as long as you give it gas, it's more likely an idle-circuit fuel issue or the choke; if it stalls anyway, it's more likely the fuel tap or the immobilizer). Urgency: no immediate danger, but an unusable bike; start with the free checks (cap, choke) before any disassembly.Diagnosis available

The clutch slips (geared bike)Engine speed rises faster than road speed, especially when accelerating hard or climbing a hill in a high gear: the clutch is slipping instead of transmitting full power to the wheel. The symptom is very distinctive and easy to recognize — when you open the throttle under load, the tachometer shoots up (the engine "races in the void") without the speed following proportionally, sometimes with a smell of hot friction material. The approach is to confirm the slipping, then narrow down the cause, from simplest to most involved. Three causes, in the order you check them. First, poorly adjusted clutch free play (no slack at the lever): the clutch stays slightly disengaged all the time and slips — a free adjustment, to do first. Next, unsuitable oil: on a motorcycle, a wet clutch sits in the engine oil, and a car oil with "energy conserving" friction-modifier additives makes an otherwise healthy clutch slip — you need oil rated JASO MA/MA2. Finally, worn clutch plates (friction material too thin/glazed, tired springs) that no longer clamp hard enough: kit replacement, an intermediate job. You tell them apart with the slip test, whether there's free play at the lever, and the context (did the problem appear right after an oil change?). Urgency threshold: a slipping clutch wears and heats up; it will eventually fail. It's not immediately dangerous, but should be addressed, starting with the free causes (free play, oil) before opening the cover.Diagnosis available

A brake drags / the wheel locks or overheatsWarning: braking is a safety-critical system, and a brake that stays applied is dangerous — don't ride until it's fixed. The bike brakes on its own, a wheel is hard to turn or slows quickly when spun, or a disc/drum gets very hot after a short ride. A brake that drags all the time wears the pads, overheats the disc and the brake fluid (risk of vapor lock and loss of braking), wastes energy, and can, in the extreme, lock the wheel while riding — hence the urgency. Main causes: a seized caliper piston that no longer retracts (drag, bluish disc), a master cylinder that doesn't release pressure (blocked compensating port: the brake stays under pressure), on a drum brake a seized cable or cams that keep the shoes extended, or more simply a poorly adjusted brake (insufficient free play, maintaining residual pressure). You tell them apart by the type of brake (disc or drum) and by tests: with the wheel lifted, does it spin freely or brake? Does the disc/drum get abnormally hot? Urgency threshold: a stuck brake that heats the wheel strongly, or a wheel that locks, requires an immediate stop — get it towed or repaired on the spot. Hydraulic causes (caliper, master cylinder) are for a professional (expert-only); free-play adjustment and mechanical drum brakes are more approachable, but always handle this vital component with rigor. Start by identifying the type of brake (disc or drum) and checking, wheel lifted, whether the wheel brakes on its own: these two simple observations quickly point to the right cause.Diagnosis available

Weak / spongy brakesWarning: braking is safety-critical — if you have any doubt, don't ride and get it checked by a professional. Braking lacks bite, the lever (or pedal) feels soft and sinks, or you need to squeeze hard to slow down. Two broad families of causes, separated by a simple test: a SOFT lever that sinks points to a hydraulic problem (air in the circuit, aged brake fluid that's absorbed water and boils under heat — "vapor lock"), while a FIRM lever with weak braking points to a friction problem (worn pads, or a glazed/greasy disc or pads). This distinction matters because it leads to very different fixes: hydraulic problems (bleeding, fluid) touch the circuit and are classified expert-only (leave to a professional), while replacing worn pads or degreasing are intermediate-level DIY jobs — but always handled with rigor on this vital component. Basic checks include: pad thickness (is there friction material left?), brake fluid level and color (clear = good, dark brown = aged), and lever firmness. Urgency threshold: failing brakes are an immediate danger. If the lever sinks to the handlebar, if the brakes no longer respond, or if you have any doubt about their effectiveness, DON'T RIDE — get it towed or repaired on the spot. Better to spend 30 euros on a diagnosis than to be unable to stop. Braking allows no shortcuts: at the slightest doubt, go to a professional.Diagnosis available

Brakes squeal / screech / judderWarning: braking is vital — if in doubt, don't ride and get it checked. Your brakes squeal, squeak sharply, grind, or you feel vibrations while braking. Severity ranges from totally harmless to a wear warning that needs attention. Most often, squealing while braking comes from accumulated brake dust or slight surface glazing — no immediate danger, fixed with simple cleaning. But a metallic grinding sound can be the wear indicator on certain pads (a small metal tab that rubs the disc to signal it's time to replace them). A constant squeal, even without braking, points to a seized caliper piston that keeps the pad in contact (friction, overheating, rapid wear). And pulsations/vibrations felt in the lever while braking suggest a warped disc. You tell them apart with three criteria: is the noise constant (seized caliper) or only while braking (dust, wear indicator)? Do you feel pulsations in the lever (warped disc)? Has bite dropped (wear) or not (harmless dust)? Urgency threshold: simple dust squealing isn't serious, but a noise accompanied by reduced bite, a brake that heats up or drags, or pulsations, should be addressed without delay — and at the slightest doubt about braking effectiveness, go to a professional. Never ignore a continuous metallic grinding: it can mean the lining is gone and the backing plate is scoring the disc.Diagnosis available

Oil leakYou find oil stains under the bike, or seepage and greasy traces on the engine. Not all oil leaks are equal: the first, decisive step is to LOCATE precisely where the oil is coming from, since this determines both the severity and the difficulty of the repair. Causes range from harmless to serious. The most common and simplest: a poorly tightened drain plug or oil filter (or a crushed/forgotten gasket), typically right after an oil change. Next come a case or cover gasket (cylinder head cover, ignition/clutch cover) that hardens and seeps over time, a leaking shaft seal — the fork seal deserves particular attention since oil on the tube reaches the disc and pads (a braking hazard), while the gearbox output seal soils the sprocket and chain — and finally, rarer and more serious, a leak at the head gasket. You tell them apart by pinpointing the source: fork tubes/front wheel? lower engine/covers? between the head and cylinder? and by noting whether the leak followed an oil change. Urgency threshold: a small leak that soils without lowering the level isn't urgent, but a significant leak (draining the sump and threatening oil pressure) or a fork leak oiling the brakes needs addressing without delay. Always keep an eye on the oil level: as long as it stays correct, you can ride carefully; if it drops, don't ride. And clean the engine to better locate an active leak: on a clean block, observed after a short ride, it's much easier to spot where fresh oil reappears, avoiding guesswork disassembly.Diagnosis available

Coolant leakYou see a colored puddle (pink, green, blue depending on the fluid type) under the bike, notice a distinctive sweet smell, and the coolant level drops. This needs addressing, since fluid loss leads to overheating, which can damage the engine. The first step is to determine whether the leak is visible and can be located, or whether the level drops with no leak apparent (a more concerning case). Causes of a visible leak: a cracked/porous hose or a loose clamp (common and accessible), a radiator or reservoir cap that no longer holds pressure (fluid overflows — an inexpensive part), a punctured radiator (impact, corrosion, often at the bottom), or a worn water pump seal (fluid drips from the weep hole under the engine — a more technical job). If the level drops WITHOUT a visible leak, and the bike overheats or gives off white smoke, suspect the head gasket (the fluid is going into the combustion). You tell them apart by looking for the puddle and identifying its source. Urgency threshold: don't ride with a leaking circuit and a low level — overheating looms, and an overheating engine can seize or crack. Major safety point: NEVER open the radiator cap on a hot engine, the pressurized fluid sprays out and causes severe burns — always work with a cold engine. If the leak is significant or the level is dropping fast, better to stop and get it repaired than risk the engine. The color and location of the puddle are your best clues: note them before doing anything, and clean the area to spot where fresh fluid is seeping from once you start diagnosing.Diagnosis available

Gears shift badly (geared bike)The lever catches, gears crunch when shifting, neutral is hard to find, or gears pop out while riding. On a bike with a manual gearbox, these symptoms have very different origins depending on whether they come from an adjustment/maintenance issue (the most common and accessible) or from the gearbox itself (rarer and more serious). The key distinction: does it CRUNCH when shifting (the clutch isn't separating the plates properly), or does it POP OUT of gear under load (internal wear)? The accessible causes: a poorly adjusted clutch (excess free play means it doesn't disengage fully, causing crunching and a stiff neutral), and worn or unsuitable engine oil — an important reminder: on a motorcycle, engine oil also lubricates the gearbox and clutch, and tired or non-compliant oil (with 'friction modifier' additives) stiffens shifting. Next comes a bent shift lever or linkage (often after a fall), which gets in the way of the lever's travel. Finally, the serious case: worn gearbox shift forks or dogs, which cause gears to pop out under load and require opening up the engine (professional work). You can tell them apart by the type of symptom (crunch vs. pop out), a clutch test (does it disengage fully?), and the context (right after a fall?). Urgency threshold: hard shifting isn't dangerous in itself, but gears popping out can catch you off guard, and forcing a crunching gearbox wears it out prematurely. Always start with clutch adjustment and oil (free/cheap) before suspecting the gearbox itself.Diagnosis available

Lack of power / the bike won't pull like it used toThe bike struggles to rev up, lacks pickup, labors on hills, tops out below its usual speed, or hesitates under acceleration. Power depends on three well-balanced, well-synchronized ingredients — air, fuel, and a spark — all inside an engine that compresses properly and transmits its force to the wheel. A loss of power therefore comes from a weak link somewhere in that chain, and the method is to rule them out from simplest to most serious. How the problem showed up already steers the diagnosis: a gradual loss over several weeks suggests slow wear or fouling (a clogged air filter, a tired spark plug, dropping compression); a sudden drop overnight suggests a discrete event (a dirty carburetor, a blocked hose, a blocked exhaust, a failed sensor). You should also tell apart two families: an engine that's genuinely down on power (revs struggle to climb) and a drivetrain that's no longer transmitting power (revs climb but speed doesn't follow — a slipping clutch). Secondary signs to watch for: exhaust smoke, a fuel smell, misfires, unusual noises, higher fuel consumption, hard starting. The 2-stroke/4-stroke distinction matters: on a 2-stroke, the exhaust carbons up and the intake clogs faster; on a fuel-injected 4-stroke, a sensor or valve (motorized throttle body, EGR) can restrict the electronics. Urgency threshold: a power loss isn't dangerous in itself, but it often signals a worsening problem (collapsing compression, a clutch eventually failing) — better to diagnose it early, while the fix is still simple and cheap.Diagnosis available

Rough idle / the bike stalls at a stopAt idle, the revs won't hold steady: they rise and fall (the engine 'hunts'), stumble, or the bike stalls outright at lights and at a stop. Idle is a tricky operating regime, because the engine is running slowly on very little air and fuel: the slightest imbalance in the mixture or the ignition shows up immediately, whereas it would go unnoticed at higher revs. Most often, the cause lies in the air and fuel supply: a mis-set idle speed, a partially blocked idle/pilot jet (the small calibrated passage that feeds the engine at low throttle openings), a false air leak at the intake that leans out the mixture, or a fouled spark plug causing misfires. On a four-stroke engine, valve clearance out of spec can also upset the idle. It's worth distinguishing: idle instability mainly when cold that improves as it warms up points to an adjustment or light fouling; idle instability all the time points to a false air leak or a spark plug; an idle that stays abnormally high and won't come down suggests a false air leak or a throttle cable that doesn't return; an idle that sags and stalls suggests a blocked idle circuit. Context matters: a problem that appeared after winter storage almost always points to a jet fouled by stale fuel. Urgency threshold: an unstable idle isn't dangerous in itself, but stalling at an intersection or during a maneuver can be — better to diagnose it early, especially since the most common causes are free or cheap to fix.Diagnosis available

Backfiring / popping from the exhaustSharp 'popping' sounds come from the exhaust (most often on deceleration, when you let off the throttle), or, more rarely and more violently, a backfire occurs on the intake side (a 'pop' in the carburetor or airbox). Either way, it's a case of poorly controlled combustion: mixture burning in the wrong place or at the wrong time. On deceleration, unburned fuel builds up and finishes burning in the hot exhaust, hence the popping. By far the most common cause is a mixture that's too lean (clogged jets, a false air leak at the intake, a cracked intake boot), sometimes made worse by an exhaust leak that draws in air there too. More rarely, a mistimed ignition or a failing spark plug causes misfires whose unburned gases explode in the pipe, and — the most serious case on a 4-stroke — a burnt exhaust valve lets ignited gases through, along with a clear loss of power. Telling them apart by timing is valuable: popping on deceleration points to a lean mixture or an exhaust leak; explosions under acceleration/load point to ignition or a burnt valve. Power level also helps: it pops but still pulls fine = mixture/exhaust; it pops AND clearly lacks power = valve or ignition. Urgency threshold: occasional popping on deceleration is rarely serious, but a backfire on the intake side can ignite the air filter (a hazard), and a burnt valve requires an engine repair. Worth diagnosing to prevent it from getting worse.Diagnosis available

Scooter: noise in the transmission (belt case)An unusual noise — a knock, a squeal, a whistle, or a growl — is coming from the transmission cover, the large cover on the left side of the scooter that houses the variator, the belt, and the centrifugal clutch. This is where the drivetrain's wear parts are concentrated, and the type of noise along with when it shows up point to the part at fault. The causes: worn/flat-spotted variator rollers (which knock on startup and deceleration), a belt at the end of its life (which squeals, then knocks, and risks breaking), a centrifugal clutch bell or shoes that judder (worn linings or a warped bell: juddering and vibration on startup), or a worn transmission bearing (which growls or whistles continuously, even at a steady speed). You can tell them apart by timing (on startup/acceleration = rollers/clutch; continuous = bearing/belt) and the type of noise (a knock = rollers/belt; a whistle/growl = bearing). Urgency threshold: transmission noise isn't immediately dangerous, but a belt at the end of its life can snap and leave you stranded, and a failing bearing can damage the transmission — not to be ignored. Most causes (rollers, belt) are routine, accessible maintenance items; the centrifugal clutch (spring under compression) and bearings (specialized extraction) are best left to a professional. Start by identifying the timing and type of noise to target the part before opening the cover.Diagnosis available

Scooter: loss of acceleration / lower top speedThe scooter accelerates weakly, no longer picks up speed like it used to, or the engine revs ("screams") without the scooter really moving forward. On a scooter, the automatic transmission (variator, rollers, belt, centrifugal clutch) is the first place to look, since these are heavily worked wear parts. The key distinction: does the engine rev up WITHOUT the scooter moving forward (the transmission is slipping: belt, centrifugal clutch), or does the engine simply lack power (a classic engine problem, like a clogged air filter)? On the transmission side, the causes are: worn or flat-spotted variator rollers (incorrect ratio shifting, loss of acceleration and top speed), a worn or cracked belt (which slips, or even snaps), a worn centrifugal clutch (slips on take-off), or a seized/gummed-up variator (the sliding faces no longer move freely). On the engine side: a clogged air filter chokes and restricts it, just like on a motorcycle. The distinction gets sharper depending on whether it's the take-off acceleration or the top speed that's suffering (take-off = clutch/belt; top speed = rollers/variator), and on the transmission's maintenance history. Urgency threshold: no immediate danger, but a belt at the end of its life can snap and strand the scooter, and a slipping transmission wears out fast. Start by ruling out the air filter (simple), then investigate the transmission based on the symptoms, keeping in mind that rollers and belt are consumables meant to be replaced at regular intervals.Diagnosis available

Scooter: it won't startThe scooter refuses to start, neither on the electric starter nor the kickstart (if it has one). As with a motorcycle, the approach is to rule out simple, free causes before taking anything apart. The scooter's first specific quirk: the brake safety switch. Nearly all scooters only allow the starter to engage if a brake lever is pulled (a switch under the lever) — this is check number one, and a very common "breakdown" is really just an unsqueezed brake or a faulty switch. After that, the same logic as a motorcycle applies: a dead battery (the starter won't turn, but the kickstart may still work), running out of fuel or stale fuel (common on a scooter that's rarely used), a fouled, flooded, or dead spark plug (no spark), and, more rarely, a failed starter motor or its relay. The distinction comes from simple tests: is the brake pulled? Does the kickstart get it going (which isolates a starter/battery problem from an ignition/fuel problem)? Does the dashboard light up normally (battery condition)? Urgency threshold: no danger, just a stranded scooter. Always start with the safety brake and the battery/dashboard condition, then fuel and spark plug, before suspecting the starter. The vast majority of scooter no-starts get solved by these basic, free or low-cost checks. The kickstart test (starts on the kick but not the button) is especially valuable: it immediately isolates an electric-starting problem from an ignition or fuel problem.Diagnosis available

The bike runs hot / overheatsThe temperature warning light or gauge climbs into the red, the fan runs continuously without bringing the temperature down, you feel abnormal heat rising from the engine, power drops off, and the engine may knock or pink. Overheating is never something to take lightly: an engine that gets too hot expands its parts beyond their designed clearances, the oil film breaks down, and you quickly end up with a seized piston, a warped cylinder head, or a blown head gasket — damage that runs into hundreds of euros. The first thing to establish is the cooling method. On a liquid-cooled motorcycle (a radiator, an expansion tank, hoses are present), there are many possible causes: low coolant, a failed fan, a stuck thermostat, a clogged radiator, a dead water pump, a head gasket. On an air-cooled motorcycle (fins only, no radiator, typical of cruisers, small-displacement bikes, and many two-strokes), there's no liquid or fan: overheating then more likely comes from too lean a mixture, a mistimed ignition, a lack of oil, or prolonged low-speed riding without airflow. Secondary signs: a smell of heat, knocking (pre-ignition), power loss, an expansion tank overflowing or bubbling. Urgency threshold: if the temperature climbs into the red, shut off the engine as soon as it's safe and let it cool down — never unscrew a hot radiator cap, the pressurized liquid sprays out and causes severe burns. Better to stop for ten minutes than to wreck the engine.Diagnosis available

Unstable handling / weaveWarning: handling is a safety matter — identify the cause before getting back on the road, and when in doubt, always have it checked by a professional. The bike weaves, the handlebar starts shaking on its own (a tank-slapper), it pulls to one side, or it feels vague and imprecise. Several systems can be at fault, and the approach goes from simplest to most serious. The most frequent and free cause to check is incorrect tire pressure (an underinflated tire makes the bike soft and unstable, an overinflated one makes it twitchy). Next come worn or deformed tires (squared-off profile, flat-spotting, a bulge) that cause weaving, worn or notched steering head bearings (tank-slapper, binding spots) — a steering component rated expert-only — and finally chassis problems (a leaking fork, a dead shock, play in the swingarm, misaligned geometry after a crash) reserved for a professional. The distinction comes from the circumstances: instability at low speed or with hands off the bars (tank-slapper: steering, tires) versus instability over bumps and in hard cornering (suspension, chassis), and from tests (pressure, steering-head play with the front wheel off the ground). Urgency threshold: pronounced tank-slap, a bike that weaves, or steering play are major safety defects — don't fight it, slow down gently (never chop the throttle abruptly during a tank-slapper, grip the tank with your knees), and have it checked before riding again. Degraded handling shows no mercy at high speed.Diagnosis available

Abnormal vibrationsThe motorcycle vibrates noticeably more than usual — in the bars, footpegs, seat, or the whole frame. Every motorcycle vibrates a bit by nature (especially singles and twins), but a sudden or gradual increase in vibration signals a problem. The key to diagnosis is figuring out what the vibrations depend on: engine RPM (they appear at a certain rev range, and are present even at a standstill while revving) or SPEED (they appear at a certain speed and follow the wheel, not the throttle). RPM-linked vibration points to the engine and its mounts: loose engine mounts or bushings transmitting normal vibration (a common and simple cause), or, more rarely, an internal engine imbalance (balance shaft, crankshaft bearings). Speed-linked vibration points to the running gear: a deformed, facet-worn, or poorly balanced tire, or a worn wheel bearing. Chain drive (worn or poorly tensioned) also generates vibration and jerkiness, especially in higher gears. Location helps too: vibration in the bars points to the front end (tire, wheel bearing); in the footpegs and frame, to the engine and drivetrain. Urgency threshold: vibration from loose mounts or a chain can be dealt with calmly, but a deformed tire, a worn wheel bearing, or a growing engine imbalance shouldn't be ignored — the running gear affects safety, and an internal imbalance can signal serious engine wear on the way. Start with the simple, accessible causes.Diagnosis available

Abnormal exhaust noise (droning, whistling, popping)The exhaust system is making an unusual noise: a buzz, a whistle, a hiss, a metallic clank, or a deeper, louder roar than it used to have. In the vast majority of cases, this is a gas leak or a damaged exhaust component, and more rarely an engine-related issue. The type of noise guides the diagnosis. A hiss or whistle, especially with 'pops' on deceleration, points to a leak: a crushed header gasket, a loose clamp, or — more serious — a cracked header (often with an unusual discoloration signaling overheating). A metallic clank that shows up over bumps and with vibration points instead to worn exhaust mounts (rubber isolators, brackets) letting the pipe knock against the frame. A noise that's become deeper and louder, more of a roar, signals a perforated or corroded silencer, or one whose internal packing has come loose. A visual inspection, done cold, is the first step: look for rust, holes, cracks, discoloration, and fixtures that move. Urgency: exhaust noise generally isn't dangerous short-term, but a header leak throws off the mixture reading (and the O2 sensor on fuel-injected bikes), can overheat a valve, and a non-compliant or overly loud silencer will fail inspection and can get you fined. Also, don't confuse a genuine exhaust noise with exhaust gases potentially entering a sidecar's cabin — and always work cold, since the exhaust burns. Better to locate and fix it early, especially a discolored header, which reveals a mixture that's too lean.Diagnosis available

Excessive oil consumptionYou need to top up the oil between oil changes, or the level drops abnormally fast. One essential point first: on a two-stroke engine, consuming oil is NORMAL (the mix oil burns along with the fuel by design). This symptom therefore only applies to four-stroke engines, where oil and fuel are completely separate and oil consumption is abnormal. Two broad explanations: either oil is LEAKING to the outside (crankcase gaskets, drain plug, seals, hoses — you'll see marks under the engine), or oil is BURNING in the combustion chamber (it disappears with no trace on the ground, but produces blue smoke). For burning oil: worn rings (blue smoke on acceleration, under load), worn valve stem seals (blue smoke on startup that clears up once warm), or a failed head gasket (often with a milky residue, white smoke, overheating). You can tell them apart with simple observations: are there oil marks on the ground (external leak)? blue smoke, and when (rings vs. valve seals)? a milky residue under the oil cap (head gasket)? Urgency: keep a close eye on the oil level and top it up — riding with a level that's too low destroys the engine. Moderate consumption is worth monitoring, but significant consumption (more than roughly 0.5 L/1000 km) or consumption that's increasing signals internal wear that needs diagnosing, especially since it can foul the catalytic converter. Track your consumption to get an objective read on the problem.Diagnosis available

Stiff / hard-to-turn steeringWarning: the steering is a safety-critical system — steering that catches or resists, especially in corners and at low speed, is dangerous. Deal with it quickly, and if you have any doubt, get it checked by a professional. The handlebar resists abnormally, catches at center, or takes unusual effort to turn. The most common cause involves the steering head bearings: when worn, they develop notches (a "tight spot" wears into the center position, where the bike spends most of its time rolling straight); when overtightened (excessive preload), they stiffen the rotation. A dry or oxidized steering head (from lack of grease) causes the same stiffness. More simply, a cable (throttle, clutch, brake), a hose, or a wire routed incorrectly can pull on the handlebar at full lock and restrict it, and a badly underinflated front tire makes the steering heavy, especially at low speed. You tell them apart with tests: with the front wheel lifted, do you feel a tight spot at center (bearings)? Does a cable pull taut at full lock (routing)? Is the front pressure correct? Causes tied to the bearings and steering head are classified expert-only (safety-critical part, steering geometry); cable rerouting and tire pressure are things you can handle yourself. Urgency threshold: steering that catches or binds can catch you off guard in a corner or during a maneuver and cause a fall — don't ignore this symptom. Start with the free checks (pressure, cable routing) before considering work on the steering head, which is a job for a professional.Diagnosis available

Hard brake lever / pedal, difficult to pressWarning: braking is safety-critical — if you have any doubt, don't ride and get it checked by a professional. The lever (or pedal) is abnormally hard, almost blocked: even squeezing hard, braking doesn't respond like it used to, or travel is very short. This symptom points to the hydraulic circuit and its main components, almost all classified expert-only since they're at the heart of braking. Three main causes: a seized or clogged master cylinder (the piston struggles to slide and return, hard lever, weak braking), one or more seized caliper pistons (oxidation, dust, aged fluid: the piston no longer moves freely, hard lever and a brake that may drag and heat up), or very old, contaminated brake fluid (thickened, with deposits or water, that flows poorly). A key test: is the lever hard right from rest with little travel (master cylinder or seized caliper), or is travel normal but it becomes very hard to squeeze (contaminated fluid)? And does the disc get abnormally hot without braking (seized caliper)? Urgency threshold: a hard brake that doesn't brake properly, or a brake that stays applied and overheats/locks the wheel, is an immediate danger — don't ride, get it towed or repaired on the spot. Nearly all the work here (master cylinder, caliper, bleeding) is for a professional: you don't tinker with a hydraulic braking circuit without the skills. Better to spend 30 euros on a diagnosis than to be unable to stop or lock a wheel while riding.Diagnosis available

Transmission / gearbox oil leakYou see traces of oil around the gearbox, the output sprocket, or, on a shaft-drive bike, the rear final drive and drive shaft. This is rarer than an engine oil leak, but shouldn't be ignored: a gearbox or final drive losing its oil risks a costly seizure. Important note: on most motorcycles, the gearbox shares the engine's oil (common sump); a "gearbox" leak is then often actually an engine oil leak located on the transmission side. On others (and on shaft-drive bikes), the transmission has its own oil. Main causes: a worn output shaft seal on the gearbox (oil seeping onto the sprocket and chain — common on 4-strokes), a gearbox case/cover seal (on the shift side or clutch side) that's failing, a poorly tightened drain/level plug (a slow leak, easy to fix), and, on a shaft-drive bike, drive shaft seals leaking (final drive oil around the rear wheel — a specialized job). You tell them apart by locating the traces: around the sprocket/chain? at the case/cover junction? at the plug? toward the rear wheel (shaft drive)? And by watching whether the oil level drops. Urgency threshold: a slow leak without a noticeable level drop isn't urgent, but keep an eye on the oil level (gearbox or engine oil, depending on the case) and don't ride if it drops — a transmission running low on oil can seize. Clean the area to better pinpoint the active leak: telling a genuine leak (seeping from behind the sprocket cover or from a seal) apart from simple chain-grease spray is key to a correct diagnosis.Diagnosis available

Exhaust fumes in the helmet or around the bikeYou smell burnt exhaust gas (sharp, irritating) while riding or at a stop, in your helmet or around the bike. Warning — take this seriously: exhaust gas contains carbon monoxide (CO), an odorless and toxic gas, along with other irritating compounds — prolonged exposure, especially in an enclosed space like a garage, is dangerous. Never run the engine in a closed space. The most common cause is a leak in the exhaust line BEFORE the muffler: a manifold gasket, a clamp, or a cracked pipe lets gas escape near the engine, and the smell rises up toward the rider instead of being carried out behind the bike. On a 4-stroke, a melted or broken catalytic converter also lets more harmful gases through, and a failed lambda sensor (or an overly rich mixture) increases unburned hydrocarbons and the smell (which then leans closer to raw fuel). You can tell them apart by timing (smell that rises while riding = leak; at a stop with a hot engine = catalytic converter/richness), the type of smell (raw fuel vs. sharp burnt gas), and a visual inspection of the exhaust line (soot marks around a joint). Urgency threshold: an exhaust leak isn't mechanically serious, but exposure to toxic gas means it should be addressed quickly, and you should never expose yourself to it in an enclosed space. A manifold leak also throws off the mixture and can overheat a valve. Always ventilate, and get it repaired without delay: when the smell shows up, its type (raw fuel or burnt gas), and soot marks around joints are the three clues that will help you pin down the cause.Diagnosis available

Smell of petrol / fuelYou smell a strong fuel odor while riding, at a stop, or when entering the garage. Warning — deal with this as a priority: gasoline and especially its vapors are highly flammable, and a leak near a hot engine, a spark, or a flame is a real fire risk. Never ignore a persistent fuel smell. The main causes: a leak in the fuel system (a cracked hose, a loose fitting, a leaking fuel-tap or carburetor float-bowl gasket — you'll see damp marks), a blocked tank vent (the tank can no longer breathe, pressure fluctuates, fuel off-gasses, and you hear a 'hiss' when opening the cap), a carburetor flooding (a float/needle valve that no longer closes, fuel overflowing the bowl — especially on 2-strokes), or, on a fuel-injected bike, a leaking injector (fuel dripping into the combustion chamber). You can tell them apart by inspection (is there a visible damp mark?), the fuel-cap test (a pressure 'hiss'?), and timing (smell at rest in the garage vs. while riding/starting). Urgency threshold: high from a fire-safety standpoint. If you see an active fuel leak (dripping), don't ride and don't start the bike until it's fixed, work in a ventilated space away from any flame, and store fuel properly. A fuel smell is never 'normal': find the source and fix it quickly. Three simple checks steer the diagnosis: a visual inspection (do you see a damp mark?), the fuel-cap test (a pressure 'hiss'?), and when the smell is strongest (at rest in the garage, or while riding).Diagnosis available

Oil pressure warning light onWarning: STOP AS SOON AS POSSIBLE AND SHUT OFF THE ENGINE. If the oil pressure warning light stays on with the engine running, continuing to ride can destroy the engine within minutes (the connecting rod and crankshaft bearings melt without pressurized lubrication). This light (often a red oil-can icon) does NOT indicate oil level, but PRESSURE: it comes on with the ignition (normal) and should go out as soon as the engine starts; if it stays on or comes on while riding, that's a critical alert. The right approach: stop, shut off the engine, then investigate — never keep riding to "see what happens." The most frequent and simplest cause is an oil level that's too low (check the dipstick first). Next come a clogged oil filter restricting circulation, a failed pressure sensor (which lights the warning even though pressure is actually fine — this must be confirmed with a gauge before concluding anything), a major oil leak that has emptied the sump, and, more seriously, a failed oil pump (no pressure at all left). The distinction comes from checks: dipstick level, oil traces on the ground, how long since the last oil change. Urgency threshold: MAXIMUM. Until pressure is restored and confirmed (or a simple sensor fault is proven with a gauge), do not ride. If the level is correct and the light stays on, have the bike towed rather than risk the engine. The golden rule: better a tow truck than a destroyed engine. This symptom only applies to four-stroke engines (two-strokes lubricate via the fuel mixture).Diagnosis available

Uneven or abnormal tyre wearWarning: tires are the bike's only contact with the road — abnormal wear affects safety (grip, handling, braking) and deserves to be understood and corrected. You notice a tire wearing unevenly: a smooth center with the shoulders still fresh (or the reverse), diagonal wear (one side more than the other), or facet/scalloped wear (a sawtooth pattern). The wear pattern is an excellent clue to the cause. Center wear most often comes from overinflation (or lots of motorway riding); shoulder wear from underinflation (or lots of cornering) — in both cases, pressure is the first thing to check, and it's free. Diagonal (asymmetric) wear points to a wheel alignment fault (chain adjusters set unevenly, an impact) or sometimes a chassis problem. Facet/scalloped wear often signals tired suspension (a dead shock or fork) letting the tire bounce. Finally, riding style and the type of trips explain part of the wear (without being a fault). The distinction comes from where the wear is located and from checks (pressure, chain adjuster marks). Urgency threshold: abnormal wear isn't an immediate danger as long as the tire stays within tolerance, but it reduces grip and often reveals an underlying fault (pressure, alignment, suspension) that needs fixing — and a tire worn to the indicator must be replaced without delay. Fixing the cause early saves the next tire from being ruined too.Diagnosis available

Vibration / pulsing in the lever when brakingWarning: braking and handling are safety matters — when in doubt, get it checked. When you brake, the lever or pedal pulses, "beats" at a regular rhythm, and you feel vibration coming up through the fork or the bars. This rhythmic sensation, which speeds up as you go faster and slows as you slow down, is characteristic: braking force varies with every wheel rotation because something in the disc/pad/wheel assembly isn't uniform. The most frequent cause is a warped brake disc (deformed, no longer perfectly flat); next come an excessively worn disc (below minimum thickness, which overheats and deforms), unevenly worn pads (a dragging caliper piston wearing one pad at an angle), and, not to be overlooked for safety, a loose wheel or wheel bearing play. The distinction comes from tests: do the pulses follow the wheel's rhythm (disc)? Are the pads worn evenly or at an angle? Is there play at the wheel (bearing)? Urgency threshold: light pulsing from a slightly warped disc still allows careful riding while getting it fixed promptly, but a badly warped/worn disc, or especially play at the wheel (bearing, a loosely tightened axle), are safety defects to address without delay. At the slightest doubt about wheel integrity or braking effectiveness, don't ride and have it checked by a professional. The rhythm of the pulses (do they follow the wheel?), pad wear (even or angled?), and any play at the wheel are the three observations that pinpoint the cause.Diagnosis available

ABS warning light on the dashboardWarning: the ABS light stays on while riding: this means the anti-lock system is disabled. Important to understand: your regular brakes keep working normally (you brake just as before), but without the assistance that keeps the wheels from locking during emergency braking or on a slippery surface. So you can still ride, but carefully: avoid very hard braking (risk of wheel lock and a fall, especially on wet ground) and have it diagnosed promptly. ABS monitors each wheel's speed via a sensor reading a toothed ring; a control unit compares the wheels and modulates brake pressure to prevent lockup. Causes of the warning light: a fouled or misaligned ABS wheel sensor (metal filings, mud, brake dust) — often fixable with a simple cleaning; a genuinely failed sensor (cut wire, broken coil); a blown ABS fuse or a loose connection; or, more rarely, the ABS control unit itself. The distinction comes from when the light turns on (right from ignition and never going out, or going out then coming back on while riding) and from inspecting the sensors and fuse. Since ABS is a safety device (expert-only safety lock), reliable diagnosis requires reading the fault code with a diagnostic tool, and work on the sensors and control unit is a professional's job. Only checking a fuse or a loose connection is accessible. Urgency threshold: no immediate danger as long as you brake gently, but don't delay getting it repaired — and above all, never permanently disable ABS just to make the light go away.Diagnosis available

Engine warning light on ('check engine')The engine malfunction light (often an orange engine silhouette, "check engine" / MIL) stays on the dashboard. This is a feature specific to fuel-injected motorcycles (modern four-strokes): a control unit (ECU) continuously monitors the sensors and engine management components, and when it detects an abnormal value or out-of-tolerance operation, it lights this warning and logs a fault code, readable by a professional with a diagnostic tool. Depending on severity, the bike may enter "limp mode": the control unit limits power and adopts a safety fuel map to protect the engine (and the catalytic converter). Possible causes are numerous and almost all electronic: a failed oxygen (lambda) sensor (poor mixture regulation), a faulty injection sensor (throttle position, intake pressure, temperature), a clogged or failing injector, or ignition misfires detected by analyzing engine speed (a tired spark plug or coil). The distinction comes from associated symptoms: power loss (limp mode)? Misfires/jerking under acceleration? Abnormal smoke? The only reliable way to pin down the exact cause remains reading the fault code with a diagnostic tool. Urgency threshold: an engine warning light with no other symptom generally allows careful riding to the garage, but a warning light accompanied by significant power loss, marked misfires, or smoke should be diagnosed quickly — riding a long time with a mixture that's out of spec can damage the engine and the catalytic converter. Except for a simple identified cause (spark plug), most of these faults call for professional diagnosis with a tool.Diagnosis available

Stiff throttle, won't return, or throttle no longer responds⚠️ Safety first: if the throttle stays open, returns poorly, or if the engine revs won't drop when you let go of the throttle, immediately kill the engine with the kill switch (red button) and stop. A throttle stuck open is one of the most dangerous faults there is: the bike keeps accelerating even as you release the grip. This diagnosis is done with the engine off and the bike stationary, never while riding. Two families of bikes, two fault logics. On a cable bike (the majority), the grip pulls a sheathed steel cable that opens the throttle butterfly; one or two return springs (at the butterfly, sometimes also at the grip) must close it instantly as soon as you let go. Typical causes: a dry cable, seized in its sheath or badly routed (rubbing, crushed when steering), a grip badly refitted after servicing (too much grease, poor alignment, fairing pinching the cable), or, more seriously, a broken or weakened return spring that no longer closes the butterfly on its own. On a bike with an electronic throttle (ride-by-wire, no cable between the grip and the engine), a faulty grip position sensor (APS) or throttle position sensor (TPS) can send the ECU into limp mode: revs stuck at idle, no or erratic throttle response, often with the check-engine light on. You tell them apart with a simple test at a standstill (does the grip return on its own, fast and fully?), by the context (right after a service or a refitted fairing?) and by the throttle type (cable or electronic). Urgency threshold: maximal for anything to do with grip return — never ride with any doubt on this point, and have it checked before getting back on the road.Diagnosis available

Tyre pressure (TPMS) warning light onA warning shaped like a tyre cross-section, often with an exclamation mark, comes on the dashboard, sometimes with a per-wheel pressure display. This is the tyre pressure monitoring system (TPMS): a small electronic sensor built into each valve or fixed to the rim continuously measures the pressure (and sometimes the temperature) and sends the data by radio to a receiver unit. On motorcycles this system isn't yet mandatory as it is on cars, but it increasingly equips premium road, adventure and touring models from the factory, and universal kits exist for older bikes. The light can signal two very different things, absolutely not to be confused: either a real pressure problem (progressive under-inflation, a slow puncture, a valve leak) which directly concerns safety and must be checked immediately with a gauge; or a problem with the system itself (an electronic sensor at end of life, unpaired after a tyre or wheel change, or simply out of sync), in which case the actual tyre pressure is fine. You tell them apart in three steps: measure the actual pressure with a gauge (the only judge, never the dashboard screen), see whether the displayed values are consistent or clearly aberrant (dashes, zero, jumping values), and recall whether a wheel, tyre or battery was changed recently. Urgency threshold: if the pressure measured with a gauge is really low, treat it like any under-inflation — it's a safety point (grip, handling, tyre overheating) to correct before riding normally. If the actual pressure is fine, the light comes from the sensor or its pairing: annoying, but not dangerous in the immediate term.Diagnosis available

Front fork oil leakYou notice a greasy film of oil on the shiny fork tube, a deposit running down toward the caliper, or a front wheel that dives and rebounds abnormally under braking. The telescopic fork is a hydraulic damper: inside each leg, oil flows through valves to slow the wheel's movement, and a fork seal (oil seal) keeps that oil from escaping along the stanchion. When the seal hardens with age, gets nicked on a spot of rust on the tube, or lets oil past because a grain of grit has lodged under its lip, oil weeps out: the fork loses damping, dives more under braking, bottoms out on bumps and — more seriously — throws oil onto the disc and pads, dangerously reducing braking. A leaking fork is an MOT failure and a real hazard: treat it quickly. Replacing the fork seals is within reach of a methodical DIYer on many models, but a pitted or bent tube (after a crash) is a job for a professional.Diagnosis available

Rear suspension bottoming out or bouncingAt the rear, the bike bottoms out over bumps (a sharp end-of-travel knock), bounces several times after a speed bump, sags too much two-up, or on the contrary stays hard as wood. The rear shock combines a spring (which carries the weight) and a hydraulic cartridge (which damps the oscillations). When the preload setting doesn't match your load, when the shock's oil is dead or leaking, when the spring has sagged after years, or when the swingarm and linkage bearings are seized, the rear end stops doing its job: degraded handling, a tyre that overheats, discomfort and accelerated wear. Many of these points can be adjusted or checked without heavy dismantling; a dead shock or worn bearings need parts but remain accessible. The key point: a rear suspension that no longer works is a genuine safety issue in corners and under braking.Diagnosis available

Gearbox jumps or slips out of gearWhen accelerating or backing off, a gear 'jumps' out: the box slots itself into neutral on its own, the bike loses drive and the revs flare, sometimes with a violent jerk. It's a mechanical symptom not to be ignored: it often starts with one gear (frequently 2nd or 3rd) dropping out under load. Causes range from the simple — a wrongly adjusted shift lever or linkage, an incorrect clutch free play that prevents clean engagement — to the serious: worn, rounded dogs (the teeth that lock the gears together), or bent/worn selector forks that no longer push the gears fully home. Riding for a long time with a jumping box worsens the wear and can break teeth inside the case. Adjusting the shifter and clutch is within your reach; dogs and forks require opening the engine, so a professional.Diagnosis available

Hard to find neutralEngine running, at a standstill, it's (nearly) impossible to find neutral between 1st and 2nd: the N light won't come on, the bike creeps forward as soon as you release the clutch, or you have to rock the machine to catch it. It's almost always linked to a clutch that doesn't fully disengage at a standstill: the plates stay slightly stuck and drive the box, which prevents the sliding gear from lining up on neutral. Common causes: wrongly adjusted clutch free play, unsuitable or worn engine oil (on wet-clutch bikes, bad oil makes the plates stick), warped or worn clutch plates, or an idle set too high. Most are easily fixed (adjustment, an oil change with the right oil); a genuinely worn clutch needs parts. Tip: look for neutral just before coming to a full stop, while the box is still turning.Diagnosis available

Stiff clutch leverThe clutch lever needs an abnormal effort, tires your left hand in traffic, returns poorly or catches. A clutch should stay light: when it stiffens, it's usually the control rather than the clutch itself. On cable bikes, the cable seizes in its sheath for want of greasing, frays or is badly routed; the free play may also be mis-set. On bikes with a hydraulic clutch (rather the bigger machines and recent models), air or aged fluid in the circuit, or a tired master cylinder, make the control spongy and stiff. More rarely, a notched clutch basket makes the mechanism catch. Most of these points are easily treated — greasing or replacing the cable, adjustment, bleeding the hydraulic circuit — and restore a nice light lever.Diagnosis available

Faulty lights or indicatorsA headlight that no longer lights, a light that fades at idle, indicators that won't come on or flash too fast: lighting is a safety and roadworthiness item. Most faults are electrical and accessible: a blown bulb, a blown fuse, a dead indicator relay (flasher unit), a corroded earth or terminal that cuts contact. A light that fades mainly at engine idle points rather to a weak charge (alternator/regulator) or a tired battery. Before any heavy dismantling, check the bulb, then the corresponding fuse, then the connections: it's often a matter of a few minutes. Beware of LEDs: an indicator that 'hyper-flashes' after switching to LED bulbs is due to a need for a resistor or a suitable relay, not a fault.Diagnosis available

Starter spins but the engine won't crankYou press the button, the starter spins (sometimes with a flaring rev or a shrill metallic noise), but the engine isn't turned over and won't start. It's different from a starter that struggles or a weak battery: here, the starter spins freely. The most common mechanical cause is the starter clutch (sprag clutch / one-way clutch) slipping: this part no longer transmits rotation to the crankshaft. The starter pinion or its teeth may also be damaged (a grinding gear noise). More serious: if the timing has jumped (belt/chain) or the engine has lost all compression, the starter turns the crank but the engine can't run normally — these cases are for the professional. You tell them apart by the noise and the context. Don't keep hammering the starter: you risk worsening the wear on the starter clutch.Diagnosis available

Burning smell while ridingA burning smell appears while riding or at a standstill with the engine hot. Depending on its nature, it points the diagnosis: an acrid 'friction' or burnt-lining smell after a hill or a lot of slipping suggests the clutch; a smell of hot plastic or rubber, sometimes with a wisp of smoke, suggests a brake staying on or oil dripping onto the hot exhaust; a sharp electrical smell (hot insulation) is the most worrying because it signals a harness or component overheating — a fire risk. Some of these causes are harmless and easy to fix (spilled oil burning off, a clutch that overheated briefly); others require stopping immediately. If there's a strong electrical smell, smoke or abnormal heat: switch off the ignition and have it checked before setting off again.Diagnosis available

The catalogue keeps growing with each new phase. If a symptom is missing, let us know from the Community page: we prioritise additions based on the most frequent requests.