How to Adjust the Carburetor on an Onan 2.8 Generator

by Mike Frees

The Onan 2.8 generator is a gasoline powered system producing 2800 watts of electricity. It is commonly used in recreational vehicles or as backup power supply for residences. If maintained carefully and tested regularly it should provide years of service. If the engine surges or runs poorly, it is likely that the carburetor needs cleaning and adjustment.

Step 1

Examine the generator or consult the owner's manual to determine the type of adjustments possible on the generator. Newer models have an altitude adjustment knob for the fuel-to-air ratio. Set the knob for the altitude at which you will be operating the generator. On these models, this is the only adjustment possible, and all other procedures must be done by a certified Onan service center. If you have an older model without the altitude adjustment knob, proceed to the next steps.

Step 2

Remove the carburetor bowl from the carburetor by loosening and removing the bolt at its bottom. Clean the bowl with carburetor cleaner and blow out the openings with compressed air. Replace the bowl on the carburetor.

Step 3

Locate the carburetor fuel adjustment screws, which may vary depending on the model. There is a main or high speed fuel adjustment, a low or idle speed fuel adjustment and an idle stop or throttle screw. If the carburetor is badly out of adjustment, set the high and low speed adjustments to their default settings by turning them clockwise until they stop and then opening them 1-1/4 turns for the high speed screw, and one turn for the low speed screw.

Step 4

Run the engine until it is fully warmed up. With the engine idling, turn the low speed adjustment screw counterclockwise until the engine speed begins to drop, then turn the screw clockwise one-quarter turn.

Step 5

Run the engine at full speed with no electrical load. Adjust the high speed screw to obtain the highest speed. Allow the engine to slow down to an idle, then apply a sudden load to cause it to accelerate rapidly. If the engine hesitates, open the high speed screw another one-quarter turn.

Step 6

Adjust the throttle stop screw so that there is approximately 1/32-inch clearance between the screw and the stop pin.

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