Cleaning the fuel tank on a dirt bike is probably something most riders have never done. It's not exactly a part of routine maintenance and can mostly be avoided by taking care when adding gas.
However, competing in an off-road race tends to let riders throw caution to the wind when entering the pits for refueling which opens the door for dust and debris. Also, restoring a vintage bike with a dirty tank or removing rust from an existing metal tank requires cleaning. Otherwise buy a new tank.
A dirty gas tank clogs fuel injectors on a 4-stroke and pollutes the carburetor on a 2-stroke. In both cases, you'll experience poor performance and eventually need to replace the jets or repair the carb. Cleaning the tank is not a pleasant endeavor so you'll want to use non-porous gloves and carry out the process in a well-ventilated area.
1. Remove the Tank
Don't clean the tank while it's still attached to the bike. Remove it. It's not hard, just a few bolts.
You'll get several schools of thought on rinsing the tank including using soap and water. That's not a good idea for several reasons especially in a metal tank. Just use gas. If you're tackling a rust job put pennies or copper BBs into the tank and shake vigorously.
Pour the rinsing gas back into a regular fuel jug, filter it by placing some nylon over the funnel or dispensing tube to catch any debris or sediment as you pour it back into the gas tank and repeat the rinsing action.
If this rinsing process doesn't fully remove all the rust you're better off investing in a new tank or finding a clean vintage tank for your restoration project.
3. Dry Tank
You actually don't need to dry the tank since gas is, well, gas. But if you cleaned the tank using something other than gas or prefer reinstalling a dry tank either set the tank aside and let it air dry since gas evaporates pretty quickly or use an air compressor to blow everything out. Meanwhile, clean the attaching bolts and the bolt holes.
4. Install the Tank
Attach the tank and fuel lines. Add fresh gas.
A nice and clean exterior
If you needed to clean the tank because of incidental dirt entering during the fueling process, ensure the fuel jug and the tank on your bike is clean and free of dirt or dust. Additionally, if you regularly race in off-road competitions, invest in a dry brake adaptor or quick-fill lid on the fuel jug. Adding a fuel filter under the gas cap isn't a bad idea regardless of riding conditions. These contraptions fill your tank in seconds, eliminate spills and encircle the mouth opening of the dirt bike fuel tank during refueling thus preventing dirt from entering.
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