Generator starts then quits when you let off the button. My '77 Model 4.0 BF series Onan developed this problem after sitting a few months. I disconnected the low oil switch and replaced the K2 relay but don't get 12v to the coil. Is the diode bad? It will run fine if I jump 12v to the coil from the battery.

Mine's a 1989 - 6.5 KW. I had a similar problem recently, & had to replace the voltage regulator - just under $200.00. If it isn't putting out the rated AC voltage it won't stay running. The VR isn't the only possible malfunction, & your older 4 KW could be different, too.

You can check the VR with a VOM that has a diode checking function. The Onan manual has instructions, but I can't help you now, my manual isn't available. If another Barthmobiler has one at hand, perhaps they could e-mail you the necessary page.

My son, the industrial electric power systems specialist who manages the installation of electrical power systems in skyscrapers, and has the latest in professional test equipment, was unable to match his readings to the manual, & couldn't assure me that it was the VR. Not wanting to embarrass him, after he went home I tried my 30 year old $3.98 Radio Shack VOM, & it matched the trouble shooting guide perfectly, so you don't have to have terribly fancy equipment to make the test.