Community Forums

tshugart3 · 05-16-2021, 03:32 PM

Hello All,

I know there are a number of threads on gensets, but I've read all I can find and haven't been able to solve this problem.

I have an Onan QG2800 gasoline generator in a Class B MH. Starting recently, the generator has major frequency/rpm swings when under low or moderate load. It starts up just fine, and actually runs steady initially on no-load, with fluctuations starting 30 sec to a minute after starting it. If I FULLY load it (A/C plus a space heater) it will steady out, but when I unload it to cool it down it has major RPM and voltage swings.

While I tried to run it once a month before recently, it hadn't gotten a lot of run time, so my assumption has been varnish in the carburetor. I've run SeaFoam cleaner through it (1 16 oz can in 2 gal of gas), allowing it to sit for overnight and then running it again. I've probably done 3-4 cycles of this with no improvement so far.

Any suggestions would be appreciated, thanks!

Tom
Tacoma, WA

THenne1713 · 05-16-2021, 06:31 PM

Typically, surging is noted MOST under load and indicates a LEAN condition, and/or FUEL delivery, but surging at no load can be a different animal. Most Onan do not IDLE under no load/ low load, so suspicion that (someone) has adjusted something wrong; WHAT is the ALTITUDE adjust on carb set to? 1) Try bringing carb altitude adjust to zero vs 5,000-10,000 (this is richer, where at higher altitude you need leaner.) 2) Otherwise, download the service manual and locate procedure to adjust governor. 2a) If If someone has adjusted carb too fast w/ no load, the SPEED GOVERNOR might be backing it down. Also helpful would be a VOLTAGE READING WHILE UNDER LOAD? 3) If you have NOT run under load for 2-continuous hours, try that and report the results? THIS will tell if you have an intermittent / failing FUEL PUMP. TYPICAL FOR Failing PUMP is it will die at some point (5-90-minutes) and NOT restart until it cools 20-30-min. That point (MIGHT BE) 90-120-min, or might be 5-60-min?) On the QG2800, I am pretty sure you can open carb bowl drain screw AFTER it dies to VERIFY that it ran out of fuel. HOPE this helps?

tshugart3 · 05-17-2021, 08:31 AM

Thanks for your response. I don't think mis-adjustment issues are what's causing the problem, as it was running fine since we got the rig and all of a sudden it isn't, without anyone doing anything to the generator other than running it periodically.

I don't know what altitude the carb is set for, as I haven't touched it or looked closely at it.

Maybe some time I'll try the 2-hr test, but I'm skeptical a fuel pump is the issue, as the genset only has about 25 hrs on it.

Thanks again for the reply!

Ray,IN · 05-17-2021, 06:46 PM

Use Seafoam in the recommended mixture(1 can>20G gas) for your gas tank with every fill-up until the genset begins to run smoothly again. It will require several such treatments.
An alternate method, if you can access the carburetor, is to trickle Seafoam directly into the running engine's carburetor without stalling the engine. This works much quicker to clean the intake system but does not clean the fuel system inside the carburetor.

autobob · 05-17-2021, 09:17 PM

You said it has 25 hours on the genset how old is the coach. In the manual you are supposed to run genset every month 20 min with a load. The gas we are using is terrible for generator especially the smaller ones if they sit long period of time. Try the seafoam first if that doesn't work may need a carb. I replaced a lot of those when I was in the R V industry.

donr103 · 05-18-2021, 09:49 PM

dont replace carb.. take it off and clean it.. maybe.. dont replace.. use the altitude adjustment knob 1st.. try it one way or the other.. little at a time.. get a spare pump and learn how to put it on.. also if adjustment does not work try carb cleaner and just that.. it is marked carb cleaner not fuel injector..( spray can) a strong flashlight and take off filter housing.. your target is those small holes , i think two little ones at top of opening and the one in center towards the back.. 1st make sure you use a new fuel filter and air filter.. some times they are over looked.. then while running and filter off put something big enough to cover carb inlet and not get sucked in,, to choke it out.. ( metal or big plastic lid)no load and breakers off.. untill eng stops.. let cool and check how running. if ok please report back.. then even if new ... change oil and filter and i hope you will be fine.. the onan carbs are meant to be cleaned.. only replace if damaged.. you will regret it..