When your engine cuts out or fails to start, it’s easy to fear the worst. But major mechanical meltdowns are rare. Most breakdowns can be tracked to one of three things: fuel supply, spark or an engine seizure.
First things first - make sure you haven’t inadvertently hit the ‘kill switch’ on the right handlebar.
To check for a spark, remove a spark plug, put the cap back on it, ensure the metal collar touches the engine block to earth it, then switch the ignition on and turn the engine over. Ensure there’s no fuel or vapour around and never touch the plug or cap with the ignition on. If there’s no spark, track the leads back to the coil, checking for cracks and secure connections. Also check the battery leads are tight.
First check you haven’t run out of petrol. If there’s plenty, check for a blockage. With carburettors, loosen the drain screw on the float bowl. If fuel flows, then it’s probably not a blockage (only do this when engine and exhausts are cold). Check the throttle cable is moving the slides inside the carb and the mechanism isn’t detached.
If the float bowl is empty, work back over the fuel lines to the tank to find the blockage. It could even be a clogged filter inside the tank.
With electronic fuel injection, about the only roadside check you can do is ensure the throttle is actuating the levers on the throttle bodies. For this, and checking many carbs, you’ll need to remove the petrol tank. Be careful not to spill petrol - pinch the line or close the end with tape or a suitable screw.
Seizures in four strokes are extremely rare but can result from working a new engine too hard or running low on oil.
Two stroke seizures can be caused by overheating, the wrong fuel/oil ratio or a malfunctioning oil pump. A partial seizure may free up once the engine cools, otherwise you're walking home.
If you feel an engine is ‘dragging’ and about to seize, whip in the clutch and keep it there until you’ve stopped.