Ever get ready to ride only to find out that you are just pouring gas onto the ground? If you have a dirt bike leak gas and you ignore the problem you are wasting money and polluting!
A common problem with older dirt bikes is gas leaking unexpectedly. Any time you have gas on the outside of the bike (anywhere but the fuel lines and carb) then you have a problem that you need to address.
Fortunately, it is usually very easy to fix a dirt bike leaking gas! Generally it is just a bad seal or gasket that is causing the leak. These are cheap and easy to replace after you find where the leak is originating.
Now let’s take a look at some of the common problems and fixes for a leaky dirt bike.
Why does my dirt bike leak gas?
Gas leaking out of the dirt bike is a symptom of a bad seal or gasket. The first step in fixing this problem is to identify the source of the leak.
The common places that a dirt bike will leak gas is out of the fuel switch, the carburetor overflow, the fuel bowl, or the carburetor drain screw. These are all easily accessible from the outside and require no major engine work.
Bonus is that the parts to fix it are really cheap!
How to find the gas leak
The first step to fixing a gas leak on your dirt bike is to identify the source. For me, this starts with turning the fuel off and drying everything off with a shop rag. Next, I will squat down next to the bike and turn the fuel back on.
If there is a drastic leak, the source will be very obvious as fuel will spill out of one area quickly. If it is a slower leak, you may need to wait until you see gas drops coming out of the overflow, or on the bottom of the carb. Follow these back up to the source of the leak and then proceed.
Gas Pouring Out of Carb Overflow
If gas is pouring out of the carb overflow, then the most likely culprit is the float valve is either stuck open or has some debris preventing it from closing.
Your carb will have a float in the bowl that rises with the level of gas in the float bowl. This float is connected to a plunger which prevents additional fuel from entering the float bowl. If for some reason this plunger is not allowed to seat in the float valve then gas will continue to come into the carb, overflowing the float bowl and running out the overflow.
Fixing it is pretty easy and involves taking the carb off your dirt bike, removing the float bowl (typically held in by 4 screws), and either cleaning or replacing the valve. Another quick trick is to try tapping on the carb bowl with the handle of a screwdriver to see if that knocks whatever is preventing the valve from closing loose.
Fuel Leaking Out of Float Bowl
Another common place for fuel to leak is going to be out of the float bowl seal itself. These leaks are generally slower than a float valve leak, and thus a little harder to spot. These manifest themselves in wet float bowls, with no obvious sign of leaking.
To fix this, you will need to take the carb off the bike (or at the very least rotate it in place by 90 degrees to give yourself access to the float bowl screws. Remove the float bowl and take a look at the gasket between in the float bowl and the carb body. This will generally be a rectangular-ish gasket roughly the size of a business card.
If the gasket looks crumbly, or a little worse for the wear go ahead and replace it. Most carb rebuild kits come with one, but you might be lucky enough to just find the gasket for the float bowl for your carb if you look.
If the gasket looks brand new, then chances are good that whoever was in the carb last time simply did not tighten the 4 screws holding the float bowl in place tight enough. Go ahead and replace the carb bowl and tighten the screws to spec.
Carburetor Drain Screw Leaking
At the bottom of most carbs there is a drain screw in the float bowl. This is used for draining the excess fuel out of the bike when you put it up for long storage. Sometimes these screws have a tendency to leak.
The fix is to either replace the screw itself, or to replace the gasket that is between the screw and the float bowl. Again, most carb repair kits are going to come with a replacement drain screw, but you might be lucky enough to find just the screw.
Of note is that on some carbs, the drain screw doesn’t exist but rather has a large bolt head in its place. This is for easy swapping of the jets. The same principal applies, these bolt heads are going to have a gasket that might be leaking.
Fuel Shutoff Valve Leaking Fuel
On most dirt bikes, there is a fuel shutoff value next to the gas tank. If you follow your fuel feed hose back to the gas tank you will find it. These fuel values are in place to allow you to turn the fuel off during storage and transportation, turn it on during riding, and some even have a RES setting which stands for reserve which gives you a little more gas to get back to the truck.
If the fuel valve goes bad, it most likely needs to be rebuilt. Rebuild kits are easily purchased online and come with everything you need. In this case, if the fuel valve is leaking, I recommend just rebuilding the entire thing instead of trying to diagnose which of the pieces of rubber is causing the leak.
If all else fails…
If all else fails, make sure to check the fuel line that goes from the carb to the fuel valve. Make sure that the connections are sound and have hose clamps on them. If the fuel line is old and brittle, just replace it. With the ethanol in most gas these days, fuel lines aren’t lasting as long as they used to.
Replacing the fuel line is a quick, cheap, and easy fix. Just take the old line off and go to your local automotive store and ask them to cut you a new piece of the same inner diameter and length of the fuel line that you just removed. You only need low pressure fuel line for carbureted bikes which is about 5 times cheaper than high pressure line. The last time I had to do this, I think it cost me a total of 2 dollars including tax.
Now that your bike is no longer leaking gas, it is time to get it fired up and start riding. If you had to completely drain the fuel out of the system, don’t be discouraged if the first startup takes a few kicks because the fuel will need to work its way down from the gas tank and fill up the float bowl before you have any shot at the engine running.
Stay safe out there!