Sludge build-up at the bottom of your motorcycle's gas tank occurs through the natural degradation of gasoline over a period of time. Sludge can clog the tank's fuel valve, hoses and, eventually, the carburettor as it continues to build up. Older motorcycles are especially likely to have large amounts of sludge within their tanks. Newer machines, however, can be affected during long periods of inactivity unless they have been prepared for storage properly. Removing the sludge from your motorcycle's gas tank will take several applications, but will reduce the likeliness of future fuel-related problems.
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Things you need
- Socket wrench and sockets
- Three-foot length of rubber fuel hose
- Gas can
- 12 Volt battery
- Rubber cap
- Rubber strip
- Heavy-duty duct tape
- 24 to 36 hex nuts
- Lacquer thinner
- Fuel stabiliser
Set the gas tank fuel valve to the "Off" position. Alternatively, set the valve to the "On" position, if a vacuum hose is attached to the back of the valve. This step does not apply to fuel-injected motorcycles.
Pull the fuel hose off of the fuel valve or fuel pump outlet. Place a three-foot length of rubber fuel hose over the outlet and place the free end of the hose into a gas can. Turn the fuel valve to the "On" or "Prime" position. Connect the fuel pump wiring to a 12 Volt battery, if you are working on a fuel-injected motorcycle. Drain the entire contents of the gas tank into your gas can.
Remove the gas tank from your motorcycle, using a socket wrench. Unscrew the fuel valve from the bottom of the tank, using a socket wrench or by hand. Do not remove the fuel pump, if you are working on a fuel-injected motorcycle. Cover the threaded fuel valve post on the bottom of the tank with a rubber cap, if the tank uses a screw-on valve, or seal the fuel valve port with a strip of rubber and heavy-duty duct tape.
Remove the gas cap from the tank, then place 24 to 36 hex nuts into the gas tank through the filler neck. Cover the filler neck with a rubber cap or duct tape. Shake the gas tank for at least 10 minutes to loosen any hard sludge deposits and corrosion build-up from the tank's inner surface. Uncover the filler neck and turn the tank upside down to remove the hex nuts. Be sure that all of the nuts have been removed before continuing. Rinse the inside of the gas tank with acetone to remove the loosened debris.
Pour 2 quarts of lacquer thinner into the gas tank, then recover the filler neck. Let the thinner dissolve the remaining sludge for a minimum of two hours. Turn the gas tank every 30 minutes until the entire inner surface of the tank has been coated with lacquer thinner.
Uncover the filler neck and pour out the lacquer thinner. Rinse the inside of the tank again with acetone. Inspect the inner surface of the gas tank with a flashlight. Repeat as needed until the gas tank is free of sludge.
Remove the rubber cap or sealing strip from the fuel valve port on the bottom of the gas tank. Reinstall the fuel valve, either by hand or using a socket wrench. Reinstall the gas tank onto the motorcycle.
Refill the gas tank completely with fresh gasoline. Add a fuel stabiliser to the gasoline to prevent sludge build-up, if the motorcycle will be placed in storage.
Tips and warnings
- Install an in-line fuel filter between the fuel valve and the motorcycle's carburettors to prevent sludge from contaminating the carburettors.
- Use care when draining gasoline, acetone or lacquer thinner from the gas tank. These chemicals will damage the painted surface of your gas tank, if allowed to soak for too long. Wipe away spills immediately with a damp towel.
- Do not work around an open flame or sparks. Gasoline is highly-flammable and cause serious injuries or damage, if ignited.
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