A flooded engine has so much fuel in the cylinder that the spark cannot light it. It happens after many failed start attempts, using the choke on a hot engine, or a carburettor float that sticks. The plug comes out wet and smells of petrol. This job dries the cylinder so the engine can start. Then find out why it flooded.
Safety
- Petrol vapour catches fire easily. No smoking, no flames, no sparks near the bike. Work outdoors.
- If fuel is dripping from the carburettor, exhaust or engine, stop and fix the leak first. See Fuel pours out of the carburettor overflow pipe.
- When cranking with the plug out, fit the cap to a spark tester or a spare plug held on bare metal with insulated pliers, away from the plug hole. A loose cap can spark and light the fuel mist.
- Do not pour or spray petrol into the cylinder to "help" it start.
- Keep cranking short. Long cranking flattens the battery and overheats the starter.
Steps
- Key OFF. Carburettor bikes: turn the fuel tap OFF and push the choke fully OFF.
- Wait a few minutes if you can. Some fuel evaporates on its own.
- Try first without removing the plug. Open the throttle fully and hold it, then crank in short bursts or kick several times. Full throttle lets the most air in to dry the cylinder. - Fuel-injected bikes: many ECUs cut fuel when you crank at full throttle. The K-Light 125 manual says that with the throttle held fully open, the engine should show signs of firing after a few seconds of cranking (PDF page 275). Check your own manual. In normal starting, the K-Light 125 manual says not to touch the throttle (PDF page 277).
- Release the throttle, key ON, and try a normal start without choke. If it fires, let it run and warm up.
- If it still will not start: remove the plug. If it is wet, dry it with a clean rag, or fit a new one. See Remove, check, gap and fit a spark plug.
- With the plug out and the cap on a spark tester, crank a few times to blow fuel out of the cylinder. Keep your face away from the plug hole.
- Refit the dry plug, refit the cap, and turn the fuel tap back ON.
- Start with no choke and a small throttle opening on a carburettor bike, or with the throttle closed on a fuel-injected bike.
Check your work
- The engine starts and idles. No fuel smell remains after a few minutes.
If it did not fix the problem
- It floods again every time: on a carburettor bike, check the float and needle valve: Check the carburettor float and needle valve. On a fuel-injected bike, a leaking injector is possible: Check the fuel injector.
- Plug dries but still no start: Check for a spark safely.
- Engine oil level rises and smells of petrol: Oil smells of petrol or the level rises. Change the oil before riding.