**Topic:** Onan BGE (F) surging constantly  
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My BGE model Onan 4K generator (F) surges when it runs. I have changed the oil, filter, air filter, and checked the plug. There is NO fuel filter to check on this (maybe removed by previous owner?). I recognize that surging is generally caused by fuel starvation. I'm looking for suggestions on how to determine if the problem is the fuel pump or the supply line. Any tips on how to test the fuel system?  
  
If I were to hazard a guess, I'd say the unit was stored without putting a fuel stabilizer in it. Then the gas forms varnish and won't run or run right 'til you take it apart and clean it. JMHO   
  
remove the fuel pump,take a small nail use it to open&close the plungers carefully while spraying w/carb cleaner or WD-40 till the plungers dont stick,reinstall,I had the same problem   
  
Dump a can of Seafoam into a fresh tank of gas in the Onan first and see if that helps...   
  
The fuel filter is screwed to the back of the fuel pump and is hard to see. The rubber fuel line connects to it.  
  
My last motor home had an Onan 4K. It surged also. I tried a number of things and finally narrowed it down to the spark quitting for a second.   
It was caused by the 10 W 30 oil that was foaming. That caused the low oil level switch to close and that interrupted the spark. When the engine slowed down the switch opened and the spark came back, then the engine sped back up.  
  
Using 30 weight oil fixed the problem. The oiling system is a splash type not a pump and it can cause foaming easily.  
  
Some oil level switches are pretty sensitive and will cause surging unless the oil is kept at the very top of the operating range.  
  
It is easy to check for this. There is a wire at the bottom front center of the engine that goes to ground. If you disconnect it and the surging stops you know the problem is caused by low oil, foaming oil, or a defective level switch.   
  
Thanks everyone. Clay, I've located the fuel pump and it appears that there is no fuel filter installed. I've crossed it with a picture of the fuel pump on the internet and I see that the fuel filter should screw into the input side of the pump. Well there is just a right angle fitting that the fuel hose plugs into. No filter. I think I'll add one once I get this guy working well.  
  
To attack the varnish issue I've been spraying B12 carb cleaner into the carb for the past day or so (letting it just sit in there). I'll start it up in a few hours and see if that helped to break down the varnish (probably not, but worth a try)  
  
Next stop will be to check that the fuel pump is actually working. Any suggestions on how to check the fuel flow short of disconnecting the metal fuel line from the carb and applying 12v to the pump and watching the fuel spurt out the metal tube (doesn't sound very safe)? I might try to pull the pump off and if so will try and clean it out, but I'd rather not take it off if I don't have to.  
  
If the fuel pump is good I was thinking about pulling the carb and rebuilding it. Is there anything else I should try before getting to that step?   
  
Gene....Does your have the winter/summer adjustment near the carb and do you have the altitude adjustment. The Onan 4K that I had, had both. They need to be set correctly for the temp and altitude.   
  
Don, it does have both and I have the air filter removed right now to access the air intake. Since it's summer weather I don't need the reheated intake air (though it exhibits the same problem with with air filter on and the switch in either the summer or winter position). As for the altitude it is set at 0 feet. I'm on the coast so my elevation isn't more than double digits.   
  
Surging is caused by one of the 16 needle holes being plugged by old gas/varnish. Carb cleanout will not remove that debris. You must remove the carb fuel bowl and unscrew the needle jet, and manually clean out with carb cleaner and compressed air.   
Fuel pump/clogged fuel filter will not cause surging. The reason is--- There is very little fuel used during APU running and the fuel supply IF shut off, will run the APU for about 30 to 45 seconds. Doug   
  
I am also waiting for Doug to reply....I have the same issue Genos   
  
For the clogged jets problem, does it make sense that I can close the choke and the surging settles out? In other words, when the generator runs it surges, but when I manually turn the choke the surging settles out. Is this typical for the clogged jets problem mentioned earlier?   
  
Yes, you can remove the bowl and jet without removing the carb. Onan does not supply rebuild parts for the carbs, but it is rare for the bowl seal and other gaskets to be destroyed for this operation. Doug   
  
Thanks Doug. I assume the bowl you're referring to is the one with the altitude adjustment on it. Safe to assume that it just unscrews? I'll have a look at the diagrams and see if I can figure it out in the mean time.   
  
Doug, so can I remove the carb fuel bowl without removing the entire carb, and if so do I need to buy any special replacement parts (gaskets, rings, etc) to replace if I remove the bowl to clean?   
  
I just sat 6 hours in the heat last week and watched a guy fix my Onan surging out of the blue. He did all of the above ideas without luck. Then he removed a black plastic dome looking part on the carb with a very thin o-ring washer under it. There was a white flapper thing inside on a spring action assembly that was sticking. He sprayed and cleaned it until it didn't stick and no problems since. Sorry I don't know the names of the parts, I hope you can follow my description. Also put SeaFoam and Chem Tool (spelling?) didn't help. He kept trying to get it running throughout every step along the way until the flapper thing. That was the problem.   
  
Looking at the blow-up diagram in the parts manual there doesn't appear to be any flapper valve looking thing. The closest I can see would be the float valve as the housing has an o-ring and the valve itself is supposed to move up and down. Would love to know if anyone else knows of a flapper valve looking thing in the carb.   
  
  
I just sat 6 hours in the heat last week and watched a guy fix my Onan surging out of the blue. He did all of the above ideas without luck. Then he removed a black plastic dome looking part on the carb with a very thin o-ring washer under it. There was a white flapper thing inside on a spring action assembly that was sticking. He sprayed and cleaned it until it didn't stick and no problems since. Sorry I don't know the names of the parts, I hope you can follow my description. Also put SeaFoam and Chem Tool (spelling?) didn't help. He kept trying to get it running throughout every step along the way until the flapper thing. That was the problem.  
  
Black Plastic dome==Carb Bowl  
White Flapper thing== FLOAT  
  
Sticking part==The float needle was sticking  
  
This would cause either flooding of the Carb or starvation of fuel  
  
NOT the cause of surging. Doug   
  
Thanks Doug, and everyone else. Removed the carb today and broke it down, removing the bowl and all of the jets. It was gummed up beyond belief. In fact I'm surprised that the darn thing would run at all with all that dirt in the bowl and blocked jets. Anyway, 2 cans of Berryman's B-12 and 4 hours later the surging in my generator is gone. Thanks again to everyone for the help.