ONAN for NCBOB I hope

[n4rsn]

Also PB Blaster sells a product called " Small Engine Tune-up"    It works great, but, I have never gotten it to work on the carbon build up on the top side of the intake valve.   
Most of our engines would run 3600 rpm, and run for 7 to 8 hours per day, 5 days a week, and they would still carbon up the intake valves.
The PB Blaster worked pretty good, but, still had to tear apart the intake after several hours.
This may not apply, with this problem, but, stick it in the back of your head, and you may be able to use it later.
Steve