The fuel cap keeps dirt and rain out of the tank, keeps fuel in, and often holds the tank vent: a small hole or one-way valve that lets air in as fuel is used. Many caps also have a key lock. A dirty or dry cap is hard to open, a cracked seal lets water in and fuel out, and a blocked vent starves the engine.
Safety
- No smoking or flames while the filler is open. Wipe up spilled fuel.
- Keep dirt out of the tank: clean around the cap before you open it, and lay the cap on a clean rag.
- Never force a stuck lock with pliers or a screwdriver. A broken cap or lock may need a new cap set, or a locksmith or dealer.
You need
- A dry lock lubricant (graphite or PTFE). Oil and grease collect dust and gum up locks.
- A new seal ring if the old one is cracked, flat or swollen. Some seals come only with a new cap.
Steps
- Wipe dust and sand from around the cap and its hinge before opening.
- Open the cap. Look at the rubber seal: it must be soft, whole and seated in its groove.
- Find the vent: a tiny hole in the cap, or a passage under a small cover held by screws. Clear dirt with a soft brush or a thin soft wire. Do not enlarge the hole.
- If the cap has a breather valve (a small flap or ball), blow gently through the vent: air should pass at least one way. If it is blocked and cannot be cleaned, replace the cap.
- Brush the lock keyway. Puff a little dry lubricant into it. Insert and turn the key several times.
- Put a light film of the same lubricant on the hinge and latch. Keep lubricant off the seal and out of the vent and tank.
- Close the cap and check it latches firmly and seals all the way round.
Check your work
- The cap opens and locks smoothly with the key.
- No fuel smell or wet mark around the cap after a ride.
- No hiss of air going in when you open the cap after a ride (a hiss means the vent is still blocked: see Check the fuel tank vent).
If it did not fix the problem
- Water keeps getting into the fuel: replace the cap seal, then see Water or dirt in the fuel.
- Lock still stuck or the key turns without opening: the lock is worn or broken. Replace the cap set.