Troubleshoot The Fuel System On A Harleydavidson

Troubleshooting a bike at the Buffalo Chip in Sturgis.

In a carbureted Harley, gasoline flows from the gas station, to the gas tank, by gravity through the petcock to the carburetor, then to the intake valves after which it explodes. In a fuel-injected Harley the gas is pumped from the fuel tank to the fuel injectors, which spray the gasoline into the intake valves. The most likely components to malfunction in a fuel-injected bike are the fuel pump or any of the multiple electronic sensors on such a bike. The fuel system on a fuel-injected Harley is diagnosed electronically. Troubleshooting the fuel system on a carbureted Harley is less susceptible to electronic gremlins and may be more illustrative of what makes these vehicles go.


1. Open the gas cap and smell the gasoline. Shine a flashlight into the tank. If you see water or diesel oil floating on top of the gasoline, you must drain the fuel from the carbureted Harley.

2. Disconnect the hose clamp that secures the fuel line to the petcock with a flat-head screwdriver. Replace the fuel line at the petcock with a 2-foot length of 1/4-inch rubber hose.

3. Insert the open end of the hose in an empty, 5-gallon gas can. Open the petcock to “reserve” and drain the fuel.

4. Unscrew the petcock from the bottom of the fuel tank with an open-end wrench. Examine and, if necessary, clean the fuel filter.

5. Reinstall the petcock with an open-end wrench. Replace the fuel line on the petcock using a screwdriver and put 1 gallon of fresh gasoline in the fuel tank.

6. Open the petcock, open the choke, put the bike in neutral and attempt to start the motorcycle.

7. Open the throttle if the bike starts and fully close the choke. Run the motorcycle until the rocker box covers are warm to the touch and allow the throttle to return to normal idle. If the engine dies at a normal idling speed take the following steps.

8. Restart the motorcycle and idle the bike with the choke pulled halfway out. If the bike runs with the choke half out, but not pushed fully in, the fuel-air mixture in the carburetor has too much air and not enough gasoline.