Community Forums

Bukiman · 12-11-2018, 12:41 PM

My 4000 Onan doesn't run at a constant speed, it will change speeds and almost to the point of stalling out, any suggestions ?

Eastham · 12-11-2018, 12:47 PM

I run some seafoam through mine and it has run good ever since. I also add it to all small engine and they run better. Can't hurt to give it a try.

Mich F · 12-11-2018, 12:54 PM

The altitude setting/adjustment might not be set right.

Ron Dittmer · 12-11-2018, 01:13 PM

Quote:

Originally Posted by Mich F

The altitude setting/adjustment might not be set right.

That's what I thought while reading the title of this thread.

Bukiman, if you don't know what that is, remove the front panel of your Onan and look at the carb. The adjustment looks like this. Grab the black knob and set it roughly to your current altitude. Sea level is 0, Denver CO is 5000, you get the idea.

Bukiman · 12-11-2018, 04:44 PM

Thanks, I'll try both if need be

avfordguy · 12-11-2018, 10:28 PM

every time. Didn't post what year and hrs,seafoam website has info on how to correct 90% of time it's a carb issue, not enough use

Bahamaniac · 01-02-2019, 11:23 PM

Try adjusting first but I had to clean out my carb. Make sure you blow out the main jet.

THenne1713 · 01-04-2019, 12:50 AM

Quote:

Originally Posted by Bukiman

My 4000 Onan doesn't run at a constant speed, it will change speeds and almost to the point of stalling out, any suggestions ?

Surging is a symptom of LEAN mixture; mine (18yo/ 220-hr/ GEN) would surge when first started, jiggling altitude adjustment back/ forth 10-20x wud help and then reset to 0 (richest); experience later found that it would SURGE/ DIE after 20-45-minutes, and not restart until cooled... and FUEL PUMP REPLACEMENT ($28 AMAZON) seems to have cured, with a successful 2-hour test run after. The other symptom that points to fuel issue was again SURGING BEFORE DYING **. I (now) suspect the initial surge was low fuel in float bowl, caused by fuel pump failure during previous run, leaving bowl dry? Fuel filter was tested and found clear/ free flowing. (*** Oil Pressure or Ignition issues should normally die immediately without surging) Luck to you. p.s. There are (some discussions) on some websites about overheat/ ventilation being the cause, (e.g. adding door vents) but if this is true, a test run with the GEN access DOOR OPEN will result in long run with no failure/ no surge? I suspect this is NOT the case... was NOT for me.

avfordguy · 01-08-2019, 09:50 PM

I bought an older (07) classic with a 4 k onan with only 25 hrs on it, dealer said they replaced the carb( yah right) constant surge, mixed seafoam 50/50with gas, ran it only on the spare gas can at 50-70% load let it sit for 30 mi utes and restarted, bunch of crap came out of tailpipe, filled by a smooth running generator, took load off and manually made the engine go to idle, about 10 times, ever since then 4k has started a performed well, you bay have to adjust the idle stop screw as mine was way out of adjustment, run with no load and adjust screw as o that it has .040 inches from carb cam to screw.
Hope this helps