How to Prime Fuel to My RV Generator

by John Cagney Nash
Light Switch and Outlet image by Towards Ithaca from

Many owners of recreational vehicles, or RVs, experience difficulty starting their remote and on-board generators. Problems occur so frequently that the RVer community has coined the nickname "trolls" to describe generators. Cummins-Onan, Generac-Guardian and Powermate are the three major generator manufacturers to the RV industry, and all the generators experience prime issues if not properly cared for. An engine's "prime" refers to the presence of usable fuel in the carburetor float bowl. If prime is lost, new fuel must be drawn from the fuel tank and the float bowl must be filled before the generator will start.

Step 1

Check the level in the fuel tank. The fuel level must be above the location of the take-off outlet to the generator fuel line, which is usually about a third of the way up from the bottom.

Step 2

Check the inline fuse. Generators are typically started with a spring-loaded rocker switch, properly called a "momentary push" switch. The prime circuit is protected by a fail-safe 5-amp fuse. A fail-safe fuse is one that blows when a problem is sensed, resulting in the circuit being left open so no electricity is present. If the fuse is blown, the prime circuit cannot function.

Step 3

Locate the prime button, which actuates a prime relay. Depressing it should illuminate the run light on the fascia or control panel, and you should hear the fuel pump run. If either function fails, check the 12-volt fuse panel. Hold the prime button in for 30 seconds or even longer if the fuel line is empty so that the pump has time to deliver fuel to the carburetor and fill the float bowl.

Step 4

Depress the momentary push switch if your generator does not have a prime button. Hold it down to run the fuel pump and the starter motor to prime the carburetor. If the generator has been unused for a long time, the carburetor float bowl will be empty and the electric fuel pump will need at least 30 seconds to reestablish a prime.

Connect a lead from the positive terminal of the battery to the positive terminal of the coil if the generator has not started. Jump-start the generator as you would a vehicle engine with a flat battery. Because current to the generator is limited, much of that dedicated power is consumed by powering the ignition circuit, the electric fuel pump and the starter motor simultaneously. The spark may be yellow-colored and weak, or "cool." A blue-colored strong, or "hot," spark is needed to start a cold generator, and maximum delivery from the pump is needed to prime a dry carburetor. A cool spark may indicate the fuel pump is also not running at peak efficiency, and jump-starting may overcome this problem.

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