51symptoms covered

144detailed solutions

100%free, no sign-up

motorcycle diagnosis: find what's causing the fault.

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

start a diagnosis explore the parts

51symptoms covered

144detailed solutions

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…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…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…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…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…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…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…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…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…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…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:…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…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…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 —…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…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…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…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…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…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…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…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…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…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…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…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…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…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…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…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…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…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…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…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…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…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…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…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…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…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…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…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…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…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…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)…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…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…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…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…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…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…Diagnosis available

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