Leaking motorcycle fuel tanks can be addressed by the do-it-yourselfer. There are many reasons for a motorcycle’s fuel tank to leak, including poor welding from the factory, rust, and damage sustained if the motorcycle is dropped or crashed, among other reasons. A leaky motorcycle fuel tank could cause a fire, and it can cause burns to the skin if the leaking fuel gets in contact with body parts. Leaking fuel can also stain or ruin clothing and gear.
Drain the fuel. Remove the fuel line from the fuel tank of the motorcycle and allow the fuel to drain into a suitable container. This is typically accomplished by using pliers to compress the wire hose retaining clamp and pulling the fuel line from the fuel tank nipple. Wipe up any spilled fuel with a clean rag.
Remove the fuel tank from motorcycle. Most fuel tanks will have a retaining bolt on the bottom center of the fuel tank (you may need to lift your seat or remove your seat depending on your particular cycle). Remove this retaining bolt with your adjustable wrench. Tip the fuel tank forward as you lift the rear of the tank, while pulling the tank to the rear.
Allow the fuel tank to vent with the cap off or opened, depending on the style of your gas cap. Aid the process by inserting the air hose from an air compressor into the tank (through the opened cap) and allowing compressed air to ventilate the tank for 10 to 15 minutes.
Remove any rust. Pour paint thinner or acetone (one to two quarts) into the tank and add a handful of small nuts and bolts into the tank. Wrap the filler hole of your fuel tank with plastic wrap and secure this with a rubber band. Shake the fuel tank and rotate to ensure the thinner and nuts and bolts make contact with all points of the tank's interior surface. The nuts and bolts will aid in dislodging any rust from the inside of the tank and create small scratches for the epoxy to adhere to.
Drain the tank. Pour the contaminated thinner and nuts and bolts into a suitable container and allow the tank to dry. Once again, compressed air may be used to aid in this process. This should take no longer than 15 to 20 minutes.
Apply epoxy sealer to the fuel tank. Mix the epoxy sealer and apply to the tank according to the directions of your sealer's manufacturer. Seal the tank's filler hole once again with plastic wrap and secure with a rubber band. Slosh the sealer around the inside of the tank to allow it to coat the entire inside surface of your fuel tank. Pour the excess sealer into a suitable container and allow the sealer inside the tank to dry according to the manufacturer's suggested time frame (typically overnight).
Replace the fuel tank. In the reverse order of the removal steps, install the fuel tank and fill with fuel. If there is still fuel leakage, take the tank to a reputable radiator shop and ask them to re-weld the tank. Many radiator repair shops also fix fuel tanks.