[bryceman]

I picked up a 316 Onan B43E with 750 hours. It was running rough until I ran a half tank of gas through it with Seafoam. It starts right up every time. When it warms up after a couple of minutes the engine seems to slightly variate (like a vroom, vroom, vroom) only when above half throttle and only when there is no load on it. It does not do it when the PTO is engaged or going up a grade. Pulling the choke out slightly does not do anything and if I pull it out too far it starts chugging from too much fuel. I tried spraying some carb cleaner over the intake manifold and did not get any reaction. I have another 316 Onan B43E with only about 200 hours on it so I know the sound is not right. It also is a little louder than my low hour 316 and has more vibration (checked the motor mounts). Plugs look good (dark brown to black but not overly sooty). Seems to have good power. Only other issue is that the ground speed slows a little when going up hill (I need to look at the hydro lever linkage). Anyone have any ideas?

 

[Hammerdown-7]

Hello Bryce
I suspect from what you have said here that you problem may very well be an Ignition issue. I would check the contact surface of the Ignition Point's to see if they are Burned or Pitted. I also would suggest that you eliminate the Ignition condenser. The Onan Ignition condenser's are well known to fail causing the Point's to burn or pit due to the High Out Put of the Ignition coil producing so much wasted spark the condenser's are the weak point of the ignition system. David Kirk performance engine's offer's a solution it is called a Point's Saver. it's cost is modest being just $32.00 shipped to your door. I have had one on my Onan for Two Year's now and it perform's flawlessly. Here is a Link to the Point's saver I hope this helps, Kurt

http://www.kirkengines.com/

 

[gzec]

Sounds like the typical surging that we all get at one time or another after 30 yrs of age. Sounds like your complete fuel delivery system needs cleaned and or changed.
Replace all the fuel lines, filter, pick ups, soak carb in cleaner etc.....

 

[knottyrope]

more than likely your slow jet in the carb is plugged up, you can remove the jet easy by removing the top of carb and the big brass screw inside should have a hole all the way through.

 

[wmgeorge]

Ditto on what Knotty just said. Use the KISS rule (keep it simple stupid) If it is plugged, then do the fuel filter, lines and tank as needed. Using the choke to make it run better is a clue its more than likely fuel related.