Onan 4KW starting issues

It's the nature of the beast. Asked the Onan Rep at the FMCA Rally in Madison, WI last summer. His fuzzy answer confirmed my conclusion that the Onan 4K carb system is a POS, and deliberately not changed to insure a revenue stream for new carbs. They consciously do not make replacement parts. If you let one set 6 months without starting plan on a new carb. I told him that expecting the old farts who own these things to start them up every 30 days was head-in-the-sand thinking. I gathered from our conversation that they won't fix it as the engine part is not made by Onan but is actually a Kuboto engine.

A shut off will help (will be putting one on the 4KW in my new MH). Unless I prime it takes 3-4 crank sequences to start. Using a shut-off and running it dry will help in hot weather. I'm considering having a "T" adaptor with outboard motor type connection. Running a small tank of half fuel-half gumout was an old marine dealer solution to fixing outboards (with tiny carb jets) that sat over the winter. Never had trouble with my outboards in the spring after learning that.

My 1999 Onan 4KW genny @ 1300 hours on the clock does the same thing. If it sits for more than a few days it takes about 8 to 10 seconds of cranking to fire up. If is sits for one day or less it starts after 1 to 2 seconds of cranking and runs fine.

I don't know if the newer Onan gennys still have an altitude compensating screw on the carburetor, but, if you have one, you might want to check to see if its set to your approximate current elevation . . . . . +-1000 feet.

Chum lee

I don't have a prime on mine so it takes me 3 tries to get it started. So yes this is normal. I think installing a one way valve would prevent the fuel from draining back into the tank making it easier to start because the fuel would stay in the line.

Effy wrote:
Yes this is normal. If it's been sitting more than a week I often prime it 2x and it starts right up. I could get away with priming it once but then it sits there and churns away trying to start. Hit the prime again and it starts immediately. If it's only been a day usually you don't have to prime it at all.

same here 2 primes if its been sitting and it fires right up

Yes this is normal. If it's been sitting more than a week I often prime it 2x and it starts right up. I could get away with priming it once but then it sits there and churns away trying to start. Hit the prime again and it starts immediately. If it's only been a day usually you don't have to prime it at all.

I also have the 4kw Onan generator in my 2015 coach and yes it does grind for sometime before starting. I was thinking about having it looked at but after talking to several people I decided to just wait and see if it improves. I like the idea of the fuel cut-off valve and was just wondering the other day if it had one. If not, I'll add it to prevent fuel from varnishing in the bowl of the carb. I try to start it at least once a month and run it hard for an hour or so.

I found that running carburetor dry before long storage helps tremendously on next restart.
On engine who did not have fuel valve, I always added one.

Yes, it is normal.

Do you know your way around a carburetor? If so, try starting it right at the genset. Hold the choke lever closed for the first 2-3 seconds while cranking. Report back. I bet it starts right up. If so, it's a choke set too lean.