Why Is My Dirt Bike Leaking Gas? How To Fix It

Is your dirt bike leaking gas? Do you smell gas when you’re on or near your bike? If so, you need to stop and figure out how to fix it. Not only are you losing gas, but it’s dangerous to have highly flammable fuel coming out of the bike when it shouldn’t be.

Most of the time it is an easy fix, but you need to have careful eyes to see exactly where the problem is coming from.

troubleshooting dirt bike carb leaking gas
Dirt bike carbs are pretty simple, but they can cause a lot of headaches if you don’t pay attention.

The Top 9 Reasons Your Dirt Bike May Be Leaking Gas Are:

  • Overfilled gas tank
  • Gas is boiling over
  • Leaking petcock/fuel shutoff
  • Fuel line is cracked
  • Carburetor gasket is bad
  • Fuel is coming out carb overflow
  • Carb drain screw is leaking
  • Sticking float
  • Dirty needle/seat

There are four main points of a dirt bike to look at when gas is leaking. The gas tank, the petcock, the gas line, and the carburetor.

  • Gas Tank
  • Petcock/Fuel Shutoff
  • Fuel/Gas Line
  • Carburetor

Let’s look at each one and all the possible problems you could run into when troubleshooting.

Gas Tank

Most dirt bike gas tanks are made out of plastic that is very thick and durable, but there’s more than one way that they can leak gas out of them. 

Leaky Holes

Although not very common and usually easy to spot, holes can cause major gas leaks on a dirt bike. Holes can from an impact such as a tree branch or a sharp rock. Holes can also happen from an unusual erosion or corrosion. All it takes is a little pinhole for gas to start coming out.

Overfilled Gas Tank?

Isn’t it nice to top off your gas tank and be confident that you can ride for hours before needing to re-fill? Well, that confidence may turn into some gas spilling out the overflow. Either from bouncing or tipping over, you may see gas coming out the overflow tube. If you see gas leaking out the tank overflow when it shouldn’t be, try adding a little less gas in the tank next time you fill up.

Gas Is Boiling Over?

Have you ridden your bike really hard on a hot day? Gas can actually bubble up and boil over if it gets too hot. This is caused by the engine getting so hot. The engine is right below the gas tank on most dirt bikes, so where does the engine heat go? That’s right, the gas tank automatically heats up once the engine is warm. If the engine gets too hot for too long then it will start to cook the gas in the tank.

What can you do to help prevent your gas from boiling over? There’s a few different ways to keep the gas cooler. If this is a consistent problem, you should get your engine running cooler

Tank Wrap

An easy way to keep the gas tank cooler is to use a thermo-heat barrier (Amazon). It’s easy to tape on to the underside of your gas tank.

An engine that runs hot may be running too lean. To fix this, it will need some jet-tuning to get the air-fuel mixture right. More gas in the mixture will help bring the engine temperature down. Going too rich will cause other side effects, such as running poorly and bogging.

Petcock/Fuel Shutoff

A leaking fuel valve, commonly known as the “petcock” on dirt bikes is not always easy to spot. You have to start with a clean and dry bike, then turn the valve on to the open position. Wait and see if you can spot where the wetness is starting from. 

Just because the bottom of the carb is dripping gas doesn’t mean that the carburetor itself is leaking. Just keep working up the chain of parts until you find the root of the problem. 

dirt bike petcock fuel valve
OEM quality petcocks are generally superior to aftermarket.

If the petcock is leaking, there are 2 possible ways to fix your problem. The fuel valve usually has a gasket or o-ring inside the assembly.  However, some assemblies are not made to be serviced, so a new complete petcock may be necessary.

Fuel/Gas Line

The fuel line is a simple piece of fuel-resistant rubber tubing that connects the fuel valve to the carb or fuel injection system. The material does not last forever, so after a number of years the rubber will harden and start to crack. This will lead to a rip or tear in the gas line that has simply deteriorated. It may start as a very slow leak, but it will soon turn into a major problem. This is why you need to figure out why your dirt bike is leaking gas right after you start smelling it on the outside of the bike.

Of course, if you don’t have the fuel line on all the way with proper hose clamps it can vibrate its way off the valve or carb spigot.

Carburetor

Last, but certainly not least, are the leaks that come from the carburetor on your dirt bike. Parts age and wear out or harden as time moves on. Rubber and paper parts dry up and crack/tear if they haven’t been used for a number of months or years. Below are the 5 different ways your carburetor could be leaking gas.

Gasket/O-Ring

The float bowl has a paper gasket or a rubber o-ring that seals the bowl to the carb body. If this is torn, cracked, or out of position, gas will seep out. First, make sure you have it properly aligned when installing it. If it still leaks, replace it with a new one. Gaskets are cheap, but you may be stuck waiting for a new one to arrive if your local shop doesn’t have them in stock.

Fuel Coming Out Overflow

Every carburetor is supposed to have overflow hoses so that if too much fuel is going into the carb it will come out of these hoses instead of flooding the engine. Any time you tip your dirt bike over, a little bit of gas will leak out the overflow, so that is nothing to worry about. 

Gas leaking from the carb overflow is common when a bike sits for long periods of time.

Gas can come out the carb overflow when the bike is tilted. This is most often caused by a float that is set too high in the carb bowl. Incorrect float height will also affect jetting, so you need to fix this right away. 

Drain Screw Is leaking

This one is pretty self explanatory. Although not all carburetors have a drain screw at the bottom of the float bowl, this is another possible point of leakage. The drain screw is a great way to quickly drain all the fuel out of your carb if needed. If it’s leaking, chances are it just needs to be tightened up again. Replace the screw if it continues to leak.

Sticking Float

A float that gets stuck in a position will act the same as the float height being off. The float can stick due to dirt from the gas tank getting into the carb float bowl. The float pin can also get gummed up from old gas sitting in the bike for too long. 

If you have problems with dirty fuel, you should consider adding a fuel filter inline so you don’t get a dirty carb and have to take it apart every so often.

Dirty Needle/Seat

The needle and seat are the parts connected to the float bowl and pin to keep the gas out of the carb until more is needed. If the needle and seat are dirty or cracked, gas will keep flowing into the carb bowl and start coming out the overflow tube. 

Dirt bike won't start because of dirty carb and jets
Dirty gas clogs up the carb jets and circuits

Sometimes these parts can be cleaned, but you will need to replace them if the problem persists. It’s not a bad idea to keep spares in your toolbox since they’re fairly inexpensive and don’t take up much space.

Kelley Fager

Kelley started riding a Honda 50 at the age of 6 years old. The passion for dirt bikes started there and grown into a lifelong pastime of riding and learning how they work. Motocross Hideout is the result of sharing his past, present, and future knowledge and experience.

Leave a Reply

Your email address will not be published. Required fields are marked *