My built-in Onan 4000 generator has about 1500 hrs on it. Problem free until last week-end at a show near Memphis.

It shut off three times overnight. It seemed to be running out of fuel. I would have tp prime it to get it started then it would run for an hour or so. The last time I got it started at about 4:30 am, it ran until we left at at 7:30 am. I stopped for fuel on the way home and started it up there and it ran fine. When we got home, I started it up and let it sit in the driveway with the air on for a couple hour and then I washed the tailer and parked it. The generator ran the whole time with no problems.

Yesterday, while riding, I started it up to see if it was OK. It started fine and ran until the ac kicked on and then it almost died, choked down and started smoking like burning oil. It didn't die and came back up and ran fine for about an hour until I shut it off. I re-started it and let it run again and it ran fine.

I had tuned it up completely before llast week-end. New plug, new air filter, new in-line fuel filter, oil change, cleaned spark arrestor. When I bought the plug, they were out of Champion plugs like it came with and that I had always used. They sold me an NGK. I did go yesterday and get a Champion plug and replaced the NGK. It started up and ran fine with the new plug, but, it was running fine with the NGK, except for the two glithes I already mentioned.

Anybody have a clue as to what might have happened or what is wrong?

Hi--You said you have 1500 hrs. on your genset--but you didn't say if you have been servicing it every 150 hrs. per manufacturers' recommendations !! You could have some fuel-varnishing taking place--depending on how often you add fuel, or how long it sits between uses.  Fuel can deteriorate in as little as 30 days.  If this is the case, you should use a fuel system cleaner made for gensets, to clean up the problem.  Afterwards, use a fuel preservative and stabilizer regularly, so the problem doesn't reoccur--especially when you aren't using the genset regularly.  Also--Onan can be reached at 612-574-5000,  hope this helps,   Zane.

Now that you mention it, yes, the trouble started when I changed the gas tank for the evening. I use 6.5 gallon baot tank that are mounted on the shelf above the generator. They have quick disconnect fittings and I just change out an empty for a full and then fill up the empty to be ready for the next change.

I started it up yesterday and let it run for a couple of hours with the AC on and still no more problems.

It has 1500 hrs on a 2002 model. We don't show in the winter anymore, so, I use a fuel preservative in the winter and start it up and let it run for 30 mins every week during the winter. In the spring, I clean the fuel tanks and run the system cleaner thru it.

I change the oil every 100 hrs., which works out to about once a month during our showing season from April thru Oct. I change the plug, air filter, fuel filter and clean the spark arrestor every 200 hrs.

Between the dualy and the generator, our fuel doesn't sit too long. Still, I'm going to go get some of the fuel system cleaner today. Thanks!

An update on the problem. I got the carb cleaner from Onan and used that. We still had a problem with the generator. It would run and work until it got warm and ten, if you shut it off, it wouldn't restart unless you adjusted the altitude screw.

I got back with Onan and was told that "if you can get it to run by turning the altitude screw, it's time to replace the carb.".

I spoke to the Onan service center in Evansville, In. and was told the same thing, except they did say that I should never have used the cleaning solution that I got from Onan.

Anyway, I took it to them last Fri., they checked it out and replaced the carb. It cost $240 parts and labor.

We used it all week-end and it runs better than ever. The carb had apparently been  malfuntioning for some time and just got to the point that something had to be done.