Draining an Evo’s Vacuum Operated Harley Fuel Valve

In this video, Bob gives us a quick overview of the Harley Davidson vacuum fuel valve. Fuel valves are found, only, on carbureted Harley Davidson models. If your Harley Davidson is fuel injected, it will have an electronic fuel pump.

A vacuum fuel valve has a fitting for a fuel delivery line and a fitting for a vacuum line. The fuel delivery line transfers fuel from the valve, directly to the carburetor. The vacuum line delivers vacuum to the fuel valve diaphragm from the motorcycles intake manifold when the motorcycle is running. The Harley fuel valve can only deliver fuel to the carburetor when the motorcycle is running. This was an important upgrade.

Earlier Harley fuel valves were manufactured without a vacuum diaphragm. They provided constant fuel delivery, even if the motorcycle was not running. It was important to turn these valves off when parking the motorcycle. Leaving on could be a problem. If the float or needle in the carburetor were to stick; the fuel valve would allow fuel to constantly flow through the carburetor. The fuel would either flow through the carburetor’s overflow to the ground, or travel through the intake manifold and into the motor. A motor full of gasoline, or gasoline all over your garage floor is a serious problem. The vacuum fuel valve eliminated the possibility of this situation.

Draining fuel through a vacuum fuel valve is easy. Disconnect the Harley fuel valve and vacuum lines. Install your fuel drain line and route it to a good fuel container. Connect your vacuum tool to the vacuum fitting and apply pressure by pumping the tool a few times.

With the vacuum tool applying pressure, and the valve turned to on or reserve; fuel will flow through the valve, emptying the tanks.

The Harley Davidson vacuum fuel valve was an important update to the carbureted fuel system. Watch this short video and you will have a full understanding of its simple form and function on your Harley Davidson.