Water is heavier than petrol, so it sits at the bottom of the tank and in the float bowl, and reaches the engine first when the tap opens. Water makes an engine cough, stall or refuse to start. A short test shows whether water is present before you drain or clean anything.
Safety
- Fuel is flammable. Work outdoors, away from flame and sparks.
- Collect all drained fuel in a container. Do not pour it on the ground or into a drain.
- Wipe up spilled fuel at once.
You need
- A clear glass jar or bottle.
- A clean cotton rag.
- A container for drained fuel.
Steps
- Turn the fuel tap OFF. Put the jar under the carburettor float bowl drain, or under the tap outlet after you disconnect the fuel line.
- Open the drain screw or tap and let fuel run into the jar. Take a good amount, so the heavy water at the bottom is caught.
- Hold the jar to the light and let it stand a minute. Water shows as separate clear drops or a clear layer at the bottom, under the petrol. Dirt and rust show as grit.
- Second test: catch some fuel on a cotton rag. Petrol soaks in. Water beads up on the surface of the cloth.
- If water is present, drain the tank and fuel line until the fuel is clean: Drain old or contaminated fuel.
- Clean the carburettor of water: Clean the carburettor. On injected bikes, change the fuel filter: Replace the fuel filter.
- Find how the water got in: a loose or cracked fuel cap, a bad cap seal, rain, condensation in a half-empty tank, or poor fuel. Fix the source: Clean and lubricate the fuel cap.
- Refill with fresh fuel from a source you trust. Do not run the bike on the contaminated fuel.
Check your work
- A fresh sample from the drain is clear, with no water layer or grit.
- The engine starts and runs smoothly.
If it did not fix the problem
- Rust or flakes in the sample: Rust or flakes inside the fuel tank, Remove rust from a fuel tank.
- Fuel is clear but the engine still stumbles: Engine turns over but will not start.