I have an older onan RV generator. It starts and runs fine for a couple of minutes. Then it starts surging. The longer it runs the worse it surges. Does anyone know a likely problem causing this?
Hi Bill,I had asked for a little clarification about how it was designed to receive fuel, without an answer I will give it my best guess. If it starts and runs fine for a few minutes, then it is running on a full fuel bowl, as the fuel in the bowl is used up and the problems begin, this tells me you have a fuel delivery problem. When the generator is inactive the restricted flow of fuel is slowly filling the bowl. There are a few solutions to remedy this problem. #1 shut the petcock off and remove the bowl from the carburetor. The float should hang down and have free movement up and down. If it stays in the full/up position, you have a fouled float needle. It will need to be cleaned or replaced also clean the orifice that the needle goes into. Inside that orifice is the main jet. I like to use a Q-tip dipped in rubbing alcohol attached to a cordless drill. Use about 3 or 4 Q-tips, the first one will come out black keep doing this until until it comes out clean. The Q-tip is mildly abrasive and won't damage the main jet, the alcohol will act as a solvent and break down any gum and varnish. Pick up a torch cleaning kit from a hardware store and clean the orifice in the main jet. Start with the smallest in the kit and work your way up until you find the one that just fits. NEVER force it into the jet. The wire that the cleaners are made from have a smooth tip at the beginning and then turn into a file a little way down, DO NOT allow the file part of the cleaner to go into the jet, this will change the dimension of the hole in the jet and ruin it. Hopefully by now you have fixed your fuel delivery problem. You can now test this procedure. reassemble the float and needle, place a container under the carburetor, open the fuel petcock. If this was the problem you should now have a smooth and steady flow of fuel, The volume should be enough to fill the fuel bowl in less than 30 seconds. If you are getting this volume, shut off the petcock and replace the fuel bowl. Open the petcock and check for leaks around the fuel bowl gaskets, after a couple of minutes if no leaks are present, start the generator and it should run smoothly. If you had fuel flow problems after cleaning the float needle and main jet, your problem is above the carburetor, it is either in the line or the tank. Today's gas contains ethanol, which acts as a solvent on fuel lines. It gums up the inside of the fuel line and the gum can migrate into fuel filters and clog them. I would replace the fuel line with an ethanol safe product like Tygon and replace or ad an inline fuel filter, get a clear one so you can monitor it. After replacing the fuel line start the generator if it is running good, you are finished. If the problem still persists, this is where I needed clarification on the fuel tank. If fuel is supplied by the gas tank on the RV there can be a multitude of problems, usually electrical or electronic. There are safeguards built into designs like this, one is to shut the generator off so you are not stranded in a remote location because your generator has used all your gas. Usually there is a sensor and a solenoid that shuts off the fuel to the generator. If you have this arrangement, you might have a bad or sticking solenoid, which would allow the bowl to fill while the generator is not in use but not allow enough fuel flow while it's running causing the surging. It could also be a bad fuel pump or air lock in the fuel line. If you have this type of setup I would suggest that you bring it to the dealer and have them diagnose the problem. I hope this helps. Good luck,Michael Burke