The bike won't start

On the Suzuki SV650, the front cylinder's spark plug well is very exposed to water spray. A blocked drain hole or a tired plug cap lets water build up around the front plug: in damp weather, the spark leaks to earth and the engine starts poorly, runs on one cylinder or misfires. The fix is simple: dry out the well, clear the drain hole, check/grease the plug cap and replace a plug or cap in bad condition. It's a common and harmless cause of capricious starting in the rain on this model.

A 12V motorcycle battery should read between 12.6V and 12.8V at rest to be considered fully charged. Below 12.4V it's weak, below 11.7V it's dead and won't turn the starter. During cranking, voltage briefly dips; if it drops below 9.5V, a cell has died and the battery needs replacing. Typical signs: a slow, labored starter, a single 'click' with no rotation, the dash going dark when you press the button, headlights dimming. A motorcycle battery lasts on average 3 to 4 years under normal use; it self-discharges naturally at 0.5 to 1% per day at rest, which explains failures right after winter storage. Source: Le Repaire des Motards, Mister Auto.

The spark plug produces a spark of several thousand volts at just the right moment to ignite the air-fuel mixture. If it's flooded with fuel (from repeated start attempts), fouled (carbon or black soot deposits), or worn (rounded electrode, cracked insulator), the spark is no longer strong enough, or is missing entirely. The engine turns over on the starter but doesn't catch. The manufacturer's gap spec (generally 0.6 to 1.1 mm depending on the model — check your manual) must be respected to within 0.05 mm. A standard plug is changed roughly every 10,000 to 20,000 km; an iridium plug can last up to 40,000 km. On a two-stroke engine, the plug fouls faster because of the premix oil. Source: NGK, Le Repaire des Motards.

Modern bikes have several safety interlocks that cut power unless they're in the right position: the kill switch (red button on the right handlebar switch) must be set to RUN; the side stand must be up if a gear is engaged; on some models the clutch must be pulled in to allow the starter to work. This is by far the most common cause after the bike has sat unused, been pushed around by hand, or simply after a moment of forgetfulness. The fault can also come from a worn or corroded sensor (side stand switch, neutral switch), especially on bikes over 10 years old or exposed to the elements. Checking this costs nothing and takes under a minute.

The tank is empty, the fuel tap is set to OFF, or the gauge is faulty and you've ridden farther than you thought. On bikes with a manual fuel tap (very common up to 2007, still found on older bikes and cruisers), there are three positions: ON (normal running), RES (reserve, roughly 3 to 5 liters left), and PRI (prime, direct gravity feed for priming). On models with a vacuum-operated tap, the tap opens automatically once the engine is running, but a worn diaphragm or a pinched hose can block fuel flow. On fuel-injected bikes, a fuel pump takes over: you should hear a brief hum when you turn the key on. Running dry remains the number-one roadside breakdown cause according to breakdown services.

If the battery is in good shape (checked with a multimeter: over 12.6V at rest, no sudden drop when you press the button) but the starter won't turn the engine over, the problem is downstream: a worn starter motor (brushes), a failed relay (solenoid), a corroded terminal, or a bad ground. A motorcycle starter draws between 100 and 200 A during that split second of cranking; a single bad connection is enough to disable it. Electrical diagnosis requires a multimeter, basic knowledge of motorcycle electrics, and the manufacturer's wiring diagram. The fix can be very simple (cleaning a terminal) or involve removing and replacing the starter motor. That's why this cause is rated expert-only: without experience, the risk of misreading a measurement or damaging the wiring justifies a trip to a professional.

Repair to be left to a professional.

On a fuel-injected bike, the ECU needs to constantly know the crankshaft's position and speed to trigger injection and spark at the right moment. This information comes from a speed sensor, called the TDC (top dead centre) sensor or crankshaft sensor, which reads the passing teeth of a toothed rotor (pulse wheel). If this sensor is dead, badly set (air gap too large), if its connector is corroded or its wiring cut, the ECU no longer receives any usable signal: it no longer knows when to inject or spark, and the engine spins on the starter without ever catching — even with fuel and a new spark plug. It's a common cause of 'it turns over but won't start' on recent injected bikes, often wrongly mistaken for a simple plug or fuel problem. Diagnosis is done with the diagnostic tool: the code P0335 or P0336 (crank speed sensor signal absent or inconsistent) confirms the fault. Before replacing the sensor, a professional first checks the connector and air gap — a bad contact is a common cause and far cheaper to fix than a new sensor. Electronic diagnosis reserved for a properly equipped professional (🔴).

Repair to be left to a professional.