If your motorcycle is leaking gas, stop riding it, shut off the fuel if you can, and keep it away from flames, sparks and anything hot until the leak is found and fixed. Gasoline vapor ignites easily, and a bike has a hot engine, a hot exhaust and electrical components, all close to the fuel system. The usual sources are the petcock, the carburetor, a cracked fuel hose, a leaking tank or a worn seal at the fuel pump or injector.
Treat every fuel leak as serious. This guide explains how to stay safe, how to find the source and what the repair involves.
What to do right now
If you discover fuel leaking, or smell gasoline strongly:
- Stop riding. If you are on the road, pull over somewhere safe and shut the engine off. Stay off the bike if fuel is dripping onto the engine or exhaust.
- Do not start the engine. Starting or restarting a bike that is leaking fuel is a fire risk, and so is using the starter.
- Turn off the fuel if the bike has a petcock with an off position. Some vacuum petcocks shut off automatically with the engine off, but not if they have failed.
- Keep ignition sources away. No smoking, no lighters, no running tools, no space heaters, no pilot lights nearby.
- Ventilate. Open doors if you are in a garage. Fumes collect low.
- Move the bike outdoors if you can do it safely and without starting it. Avoid pushing it through a space where fuel is running.
- Contain the fuel. Use a drip pan and absorbent material. Do not wash fuel into storm drains or the ground.
- If there is fire or a large spill, get away and call emergency services.
NHTSA's motorcycle safety page lists checking under the bike for oil or gas leaks as part of a pre-ride routine, which is a good habit before every ride. Our pre-ride inspection checklist covers it.
When to stop riding
Do not ride the bike if:
- Fuel is dripping, running or spraying from anywhere.
- You can see wetness on the tank seams, the fuel line, the carburetor or the fuel rail.
- You smell gasoline while riding or after shutting off.
- Fuel is visible on the engine or exhaust.
- Fuel leaks when the bike leans on the side stand, or when you lean it for a turn.
A stationary leak can become worse with vibration, heat and sloshing in motion. Have the bike towed or trailered to a shop. See motorcycle towing options if you need help moving it.
Where gas leaks from: a quick guide
| Where fuel appears | Likely source |
|---|---|
| Drips from under the tank, on the petcock | Petcock seal or diaphragm, loose fittings |
| Drips from a hose at the carburetor | Cracked or loose fuel line |
| Fuel running from the carburetor overflow tube | Stuck float or needle valve |
| Wetness on tank seams or below the tank | Rust-through, cracked seam, damaged tank |
| Fuel smell near the filler cap, wet spot around it | Cap gasket or breather, overfilling |
| Wet fuel rail, injector or fuel pump area on an injected bike | O-ring, seal or fitting leak |
| Fuel in the air filter box or coming from the intake | Carburetor flooding |
| Fuel in the oil | Carburetor or injector leaking into the engine, check oil smell |
Common causes of a motorcycle gas leak
Petcock problems
The petcock is the valve that opens and closes the fuel supply from the tank. Seals and diaphragms wear over time. Symptoms include fuel dripping from the petcock or the carburetors filling when the engine is off. On vacuum-operated petcocks, a failed diaphragm can let fuel pass even with the engine off. Replacement petcocks or rebuild kits are common repairs.
Carburetor overflow
If a float sticks or a needle valve does not seat, fuel keeps filling the carburetor bowl and runs out the overflow tube. This often happens after a bike sits with old fuel, and it can also drain fuel into the engine. A leaking carburetor also makes the bike hard to start and can foul plugs. See how to clean a motorcycle carburetor. If the engine has taken in fuel, you may be dealing with a flooded motorcycle engine.
Cracked or loose fuel lines
Rubber fuel hose hardens, cracks and swells with age and heat. Clamps loosen. Inspect the hose from tank to carburetor or injector rail along its whole length, and look for cracks, wet areas and stiff, brittle rubber. Use hose and clamps rated for fuel. Do not substitute generic vacuum tubing or general-purpose hose.
Tank damage and rust
A tank can leak at seams, around the sending unit or fuel pump flange, or through rust holes. Dents from a crash can also crack the seams. If the bike has been in a tip-over, look at what to check after a motorcycle crash. Fixes range from sealing a minor leak (a poor long-term solution) to replacement.
Filler cap and vent system
A worn cap gasket, a damaged cap lock or a clogged vent can let fuel splash or siphon out. Fuel running from the cap on a tilt or in a turn is a safety issue. On bikes with an evaporative emissions system, damaged canisters and hoses can also seep.
Fuel pump, filter and injector seals (fuel-injected bikes)
Injected bikes run fuel at much higher pressure than carbureted ones. Leaking O-rings at the injectors, fuel rail fittings, the pump flange or the in-line filter are more serious because the fuel can spray. Do not attempt to loosen high-pressure connections without depressurizing the system per the manual. This is typically a job for a shop.
Ethanol and old fuel
Gasoline containing ethanol can degrade some older rubber and plastic parts, and fuel that sits can gum up and cause stuck floats and needles. Many riders use a fuel stabilizer for storage. Our winterizing guide covers storage, and the right fuel and parts for your bike are listed in the owner's manual. Check with the manufacturer if you are unsure.
How to find the source of a leak
Do this outdoors, with the engine off and cool, and no flames or sparks nearby.
- Clean the area. Wipe the tank, lines and carburetor so fresh fuel stands out.
- Smell and look. Use a flashlight and a mirror. Gasoline leaves a clean, wet look and evaporates quickly, leaving a stain.
- Check from the top down. Start at the filler cap, then the tank seams, then the petcock and the fuel line.
- Open the fuel on and off. If the leak stops when the petcock is off, the leak is downstream of it.
- Check overflow tubes. Look for fuel at the carb vent and overflow lines below the carburetor bowls.
- Look at fuel level and oil. If the oil level is rising or the oil smells of gasoline, fuel is getting past the carburetor or injector into the crankcase. Do not run the engine, and have the oil changed.
- Lean the bike on the stand or lean it slightly to see if the leak is position-dependent.
Do not use open flames or a pressurized spray to hunt for leaks. If the source is not obvious, a shop can pressure-test the system safely.
Fixes by cause
| Cause | Typical fix |
|---|---|
| Petcock leak | Rebuild kit or replace petcock |
| Stuck float or needle valve | Clean or replace the float needle, and set float height |
| Cracked fuel hose | Replace with fuel-rated hose and new clamps |
| Cap gasket or vent | Replace gasket, clear vent line |
| Tank leak | Repair by a qualified shop, or replace tank |
| Injector or fuel rail O-ring | Replace seals, following the service manual |
| Fuel pump flange leak | Replace seal or pump assembly |
Typical repair costs
Costs vary by bike, region and shop.
| Repair | Typical range |
|---|---|
| Fuel hose and clamps | About $10 to $60, plus labor |
| Petcock rebuild or replacement | About $30 to $200 for parts, plus labor |
| Carburetor clean and float service | About $100 to $500, see our carburetor cleaning cost guide |
| Fuel pump replacement | About $200 to $700 or more |
| Tank repair or reline | Several hundred dollars, varies widely |
| Replacement tank | Varies widely, from used to new OEM |
Our motorcycle repair cost guide explains how shops price this kind of work.
Leaks, smells and related problems
A fuel smell is not always a leak at the tank. Rich running makes the exhaust smell of gasoline and can blow black smoke, see motorcycle smoking from exhaust. If the leak is oil rather than fuel, our guide to finding the source of a motorcycle oil leak can help you tell them apart. Gasoline thins and smells different from oil, and it evaporates faster.
When to see a mechanic
Take the bike to a shop if:
- You cannot find the source of the leak.
- Fuel is leaking from the tank, a fuel pump or injector area.
- The bike is fuel-injected and you are not sure how to depressurize the lines.
- Fuel has made its way into the oil.
- There has been fire damage, melted wiring or a strong smell that will not go away.
- The leak returns after a simple repair.
A fuel system repair is one place where it pays to have a professional check your work. Look for motorcycle diagnostic shops and general maintenance shops. You can also browse motorcycle repair shops in Michigan or a city like Detroit. If the bike has an open safety recall for the fuel system, the manufacturer may repair it at no charge. Check NHTSA's recall lookup by VIN, or read our guide on how to check motorcycle recalls.
Frequently asked questions
Is a motorcycle gas leak dangerous?
Yes. Gasoline vapor ignites easily, and a leak near a hot engine, exhaust or electrical parts can start a fire. Even a small leak should be treated as a reason not to ride or start the bike until it is fixed.
Why is gas dripping from my motorcycle when it is parked?
Common causes are a failing petcock, a stuck carburetor float or needle valve, a cracked fuel line or a leaking tank. Fuel can also overflow from a carburetor bowl vent when a float sticks.
Can I fix a leaking fuel line myself?
Replacing a visibly cracked rubber fuel hose is a common DIY job if you use the correct fuel-rated hose and clamps and work safely. Injected bikes with high-pressure lines and fittings are better left to a shop.
What should I do with gas that leaked into my garage?
Ventilate the area, remove ignition sources and soak up the fuel with absorbent material. Do not pour gasoline down a drain, and dispose of soaked material through your local hazardous waste program.
References
- NHTSA: Motorcycle safety (check under the bike for oil or gas leaks) (nhtsa.gov)
- NHTSA: Recalls lookup by VIN (nhtsa.gov)