For several years, I have been attempting to fix a white smoke problem with our onboard onan 4000 generator and am writing to offer hope to others with this problem. I have read countless posts by frustrated generator owners, and felt equally frustrated with our rig. The generator always started and ran super smoothly, and then began blowing a huge amount of embarrassing white smoke after about 5 minutes. We generally have only used the generator to run the microwave for the few minutes before white smoke makes it appearance and then would sheepishly shut it down. At first I thought it was a carb problem (too rich) as the smoke didn't smell like burned oil but after putting on a new carb, the darn thing still smoked like the dickens. This year, I again started trying to remedy the situation with a new breather (reed) valve, but to no avail. Feeling helpless and discouraged, I removed the two exhaust drain plugs and got a big surprise...oil started running out. After thinking this through, I decided to examine the valves a bit more closely. After removing the necessary parts, imagine my surprise to find the exhaust valve was missing its valve seal. There were no parts of a destroyed seal anywhere inside the valve cover, so I have to assume that there was never a seal installed on this unit. After purchasing a new seal, installing it, and adjusting the valves (all things that anybody else can do if I can) the thing runs perfectly and doesn't blow any white smoke. Hope this helps someone else in the same predicament. Check the valve seals.
