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How to Remove Cycle Tank Gas Varnish

by Patrick O'Donnell

When gas sits unused in a fuel tank for a long period, it forms a varnish that can clog fuel systems. Your motorcycle may run rough or not start at all. It's relatively easy to fix, however.

Step 1

Drain fuel from the tank and lines into a suitable container, such as a gas can.

Step 2

Remove the gas tank and, if applicable, any filter or fuel-sending unit inside the tank. See your motorcycle's instruction manual or a repair manual for instructions specific to your motorcycle.

Step 3

Plug up the hose or valve where the fuel exits the tank. It's often easiest to attach a small length of old fuel line that you don't need to the tank, then plug up the fuel line with anything that fits. Although you can buy plugs for this purpose at an auto parts store, a pencil can work in a pinch, or you can use cork or masking tape.

Step 4

Following the instructions on the bottle, pour the fuel cleaner, acetone or lacquer thinner into the tank. In some cases, the cleaner must be allowed to soak for several hours. However, if you're using acetone, add the BBs, marbles or nuts. Remember to keep track of how many you put inside the tank. If you don't get them all out, they can cause serious problems.

Step 5

Close the lid of the tank and shake it, then allow it to sit for about 15 minutes on one side. Flip it over and allow it to sit for about 15 minutes on the other side. Shake again, then drain the fluid into a suitable container.

Rinse the tank well with hot water, then dry it by either allowing it to sit in the sun for several hours or by using a hair dryer (ensuring that there is no flammable gas or cleaner residue in the tank first). The tank should now be clean, dry and ready for re-installation.


  • Don't let cleaning solvents or acetone come in contact with rubber components, including fuel lines. Most cleaning solvents will eat through rubber. Gas and fuel system cleaners are extremely flammable. Avoid sparks and open flame! Dispose of old gas and cleaning fluids properly. Contact an auto parts store, your local recycling center or a car or automotive or motorcycle repair shop for locations that accept used fuel. Avoid contact with gasoline or fuel-system cleaners. These are hazardous and cancer-causing materials. Wear proper safety gear. At the very least, wear neoprene gloves and eye protection. Never mix different types of fuel system cleaners.

Items you will need

  • Acetone, lacquer thinner or a fuel-system cleaner designed to remove varnish
  • Set of SAE or metric wrenches
  • Empty gas can
  • Rags
  • BBs, marbles or nuts
  • Neoprene gloves
  • Disposable clothes

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