Check the fuel tap, lines and flow

Home mechanic (basic tools) · Time: 20 to 45 min (estimate) (estimate)

This job proves whether fuel can flow from the tank to the carburettor, and finds leaks, kinks and blockages in the tap and hoses. On a carburettor bike it is the first fuel check after "is there fuel in the tank". On a fuel-injected bike you only inspect the hoses from outside; the line is under pressure and is not opened at home.

Safety

• Work outdoors or in a well-ventilated place, away from flames, cigarettes and sparks. Keep a fire extinguisher (ABC dry powder) near you.
• Let the engine and exhaust cool first. Fuel dripping onto a hot exhaust can catch fire.
• Wear safety glasses. Catch all fuel in a clean container and wipe spills at once.
• Fuel-injected bikes: do not pull a fuel hose off. Residual pressure can spray fuel. Leave pressure work to a workshop.

You need

• A clean, clear glass jar (to see water or dirt) and a proper fuel can.
• Hose clips, a new hose of the same inside size and fuel-rated material, or a tap O-ring if you find damage.

Steps

1. Identify your tap. A manual tap has OFF, ON and RES (reserve). A vacuum tap has a small vacuum hose to the engine and ON, RES and often PRI (prime). Most fuel-injected bikes have no tap; the pump is in the tank.
2. Look along every fuel hose with a torch. Replace any hose that is cracked, hard, swollen, sticky or kinked (K-Light 125 manual: wear, cracks or swelling mean replace).
3. Check every clip is tight and every joint is dry. A wet joint or a fuel smell means a leak.
4. Carburettor bikes, flow test: turn the tap OFF. Pull the hose off the carburettor end and put it into the jar.
5. Turn the tap to ON. Fuel should run in a steady stream. Then try RES; it should also flow. Turn the tap OFF again.
6. Vacuum tap: fuel only flows on ON when the engine sucks. Use PRI for the test if it has one. If it has no PRI, a workshop can apply gentle vacuum to the small hose. No flow on PRI means a blocked tap or filter.
7. Look at the fuel in the jar. Bubbles or a separate clear layer at the bottom mean water. Brown or cloudy fuel or a varnish smell means old fuel. Go to Drain old or contaminated fuel.
8. Weak flow on both ON and RES: remove the fuel cap and test again. If flow improves, the tank vent is blocked: see Check the fuel tank vent.
9. Still weak: the tap strainer or inline filter is blocked. Drain the tank, remove the tap, and clean its strainer and sediment bowl by blowing air from the inside out. Fit a new O-ring or gasket if the old one is flat. See also Replace the fuel filter.
10. Refit the hose and clip. Turn the tap ON and check every joint for drips before starting.

Check your work

• Strong flow on ON and RES, no drips at the tap, hose ends or carburettor.
• No fuel smell after five minutes with the tap ON.
• The engine starts and runs without stopping after a few kilometres.

If it did not fix the problem

• Good flow to the carburettor but the engine still starves: see No fuel reaching the carburettor and Clean the carburettor.
• Fuel-injected bike with no pump buzz: see Check the fuel pump.
• Leak from the tank seam or tap body that clamps will not fix: replace the part or take it to a workshop.