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Why Is My RV's Generator Revving Up And Down?

by Perry
(Barto, PA)

What causes the generator to rev up and down? The only thing I am using is 1 interior light at the time. When the generator acts up like that, the lights blink as well.

ANSWER: Greetings Perry thanks for submitting your question on our Ask An RV Question Page.

There are two possible problems that could be causing this revving up and down of your RV's generator. The first is a fuel problem or possibly a problem with the governor on the generator. I am inclined to believe your problem is in all likelihood a fuel problem.

Since you don't tell me, I am going to have to assume that your generator is a gasoline generator. There are two important facts that you need to know about your generator.

1. Generators need to run at least once a month for a couple of hours with a load on them. This is called "Exercising Your Generator" and generators love and need exercise.

2. The carburetor’s on generators that do not get exercised regularly can get all varnished and lacquered up in as little as a month's period of time. Based on your description, this is what I think is causing your generator to surge up and down.

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Fixing It Since I do not know how mechanically inclined you are or what make or model your generator is; I can only give you some general guidance here.

The first thing I would do is check all the fuel lines leading to the generator for leaks and/or cracks. If all the fuel lines seem good, the next step I would take is to change the fuel filter leading to the generator. Once you check the fuel lines and change the fuel filter try running the generator and if the problem disappears consider yourself very lucky.

If the fuel filter does not correct the problem, then you are going to have gain access to the generator's carburetor, remove it from the generator and soak it in some Carburetor Cleaner to try to get it cleaned out. If that works then you should still consider yourself lucky.

If that doesn't work then depending on the make and model of your generator you will have to either rebuild the carburetor or buy a replacement carburetor.

If everything I described above is something you are not comfortable doing yourself then you need to take your RV in and have a Qualified RV Technician diagnose and repair the generator.

Preventing The Problem From Happening Again The easiest way of preventing this gummy fuel problem is to run
(exercise) your generator for at least 2 to 3 hours once a month. When I say 2 to 3 hours, I don't mean 1 hour one day and 1 hour the next day. I mean 2 to 3 hours straight.

When you exercise your generator it needs to have an electrical load on it. For example if you are exercising your generator in the summer, you should run at least one of your RV's roof air conditioners. If you are exercising your RV's generator during the winter you should plug in at least one or two 120 volt space heaters inside the RV. Running a TV set or a coffee pot is not going to provide enough electrical load to properly exercise your generator.

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What if your RV is in storage for more than a month and you are unable to exercise the generator on a monthly basis? The least you can do is get some Sta-Bil Fuel Stabilizer and add the proper amount for your RV's fuel system. Once you have added the fuel stabilizer to the RV's fuel system you should run your generator for about 10 minutes to make sure that stabilizer makes it to the generators carburetor. You should always use a fuel stabilizer in your RV if it is going to sit for a month or longer.

Just a reminder! Using a fuel stabilizer does not take the place of exercising your generator, but it does help if it is impossible for you to exercise your generator.

As I said earlier problems with the generator's governor could also cause surging problems. The bottom line is the only way you will know for sure is by taking your RV in and having it looked at.

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Do you have any suggestions or comments on this topic? You can add them to this page by clicking on the "Click Here To Post Comments" link located near the bottom of this page.

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Comments for Why Is My RV's Generator Revving Up And Down?

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Surging Generator
by: Anonymous

I agree with the earlier comment...after performing all of the above including removing the fuel gauge and filter and lines, cleaning the carb...it was just an adjustment...1/16th of a turn on the throttle screw with a Phillips. So try that first before the more time consuming fixes.

Onan 5500 Gen Surging
by: Anonymous

I read alot of diagnosis on the reason for my generator was surging. I read the carb is varnish, the fuel filter is clogged, and the fuel pump is not working right. Well I did all the repairs and found that my idle screw had backed off and the throttle was closing all the way causing the surging. This was not mentioned once in my search and would have saved me alot of time. So if you experience a surging generator at idle check the idle screw first. Hope this helps.

Idle issues Onan generator
by: AL

I just removed disassembled the carborator and lacquered it was.... Sea-foam and carborator choke cleaner did the job.. Oh it's a 5500 Onan... She's running but the idle keeps jumping for about 12-tto 15 jumps then she runs quietly and steady.... Could it be the carborator still has lacquer in it??

Why Is My RV's Generator Revving Up And Down?
by: Tom Kale

Solution: Propane fueled digital inverter generators made by BEEM Outdoors, they are just great. Propane fuel never goes bad, never clogs up fuel lines or carburetors, etc..., and is cheaper than gasoline or diesel. If using a 5th wheel or travel trailer of sorts, most already have propane fuel tanks on board.

Possible quick and easy fix.
by: Tom

When I got my bus it had been sitting for quite some time, and the generator wouldn't even start. I took the carb out but was unable to dissasemble it fully, I could only get the bowl off. I took that off, cleaned it out and sprayed nearly a full can of carb cleaner. I was finally able to start it but it would die and or surge.

The problem with a surging generator is the surging causes the sine-wave to get all wonky. On mine I put some seafoam in the tank, some more in the bowl and I let the generator run with that for about an hour, when it smoothed out I started turning things on, at first a few lights. About 10 minutes later I turned off everything and turned on one AC. About 20 minutes later it stabilized,

I slowly started adding more and more until I turned all but the first AC off and then turned the second AC on. Again 20-30 minutes later it stabilized, I then turned everything else on, and left everything on for about an hour to an hour and a half.

Best of luck with your generator,

Additional thought and suggestions
by: Shawn

Quite often, as the first comment indicates, a surging gasoline small engine is a result of an air leak. Inspect all your fuel lines, carburetor gaskets, etc.. carefully for cracks and damage.

One trick that I've found useful in locating hard to find leaks is to take a small canister of pressurized gas (propane, butane, etc...) and use it to find any air or vacuum leaks. You simply open up the valve on the can, but do NOT ignite the gas. Start by directing the gas around the carb and fuel lines. If the engine straightens out, you've located the area of the leak.

Fuel Line
by: Anonymous

I had the same problem with my gas powered generator and after doing all the above mentioned steps including changing the spark plugs. I found out that it was a cracked fuel line (hose) located on top of the fuel tank. It was cracked right where it made a bend so it was easy to spot. I replaced the entire line (about 7 feet) and now she purrs like a kitten!!!

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