Yet another Onan running like **** thread. HELP!

[funk-o-meter]

Hi all!

Short version first:

1999 Onan MicroLite 4k
Been sitting for years
new fuel pump
new fuel filter
new air filter
oil change
pulled and cleaned carb twice
two bottles of Sea Foam

Runs like **** with no load.
Runs slightly crappy with a load. Engine "Hunts."


Long version:

Got an old 1999 Four Winds class C out of Mom's yard and have been working on it. Lots of work. Lots and lots of work. It's been sitting for at least 5 years seeing little to no action. All the fuel was varnish. Plumbing cracked. Brakes sticking, coils where shot. Same old RV Blues.

My current issue, however, is with the genset. Onan Microlite 4k. I replaced the fuel pump, fuel filter, air filter, and cleaned the **** out of the carb a couple of times and got it back up and running but it runs like ****. It "hunts" without a good load on it but runs reasonably well with the air conditioning on with only a few hiccups every now and then. Course when the AC kicks on it dips down momentarily to like 80V which also sucks.

From what I've read this points to the carb being dirty, or possibly the carb needing adjusting. So I worked on the carb... a lot. I exercised the generator several times for an hour each time. Ran like ****. So I pulled the carb off completely, sprayed and wiped the bejesus out of it. I unstuck the fuel shut off solenoid and tested it with a 12v source. Cleaned the float and needle and made sure they move well. Linkage and butterfly valves all move easily. Did all this and ran a can of Sea Foam through it in a 50/50 mix of it and high octane gas. It still ran like ****. So I pulled just the carb bulb, float and needle and cleaned everything again, did another round of sea foam and gas. Same deal. Visual and from what I can test the carb should be good.

I can't really do a carb adjustment because it's only got a throttle stop screw and a main/altitude adjustment screw on this carb. No idle adjustment screw. Also, I don't have a meter that reads frequency. I have no idea the history on this genset or if it's ever been adjusted by anyone. I do know the main/altitude adjust screw was very loose and only a few turns from popping out when I had the carb removed. And the main adjust screw "limiter cap" is missing. I followed the service manual and set the main adjust by turning it until I felt resistance, then backing it out two full turns.

Is there anything else I can do before I just take it to a Cummins repair shop? I'm about at my end with this thing. Got them Old Onan Blues. Lawd lawd....

Any advice is greatly appreciated.

[funk-o-meter]

New one came with the new carb. I suppose I could still test it though. Doesn't explain blowing fuses though.

[PaulJ2]

How about the fuel shutoff solenoid intermitentent/bad? Or is it part of the new carb?

[maillemaker]

I recommend you cruise over to the Onan experts here:

https://www.smokstak.com/forum/forumdisplay.php?f=1

You will need to post your genny model number and serial number.

Steve

[funk-o-meter]

Well, I got a shiny new carb installed today but it did absolutely no good. Genny still ran like **** and konked out after a minute. Actually worse than before. I checked for fuel at the carb and it looked like I might have a fuel line issue, so I ran a short new fuel line to a small gas can down below the rig. Same performance, it would run like **** for a second and stall out.

But wait, here's the best part! Out of the blue it's now blowing 5amp fuses every time I hit the start button. Awesome! I love working on this thing!

Somebody help me out here before I just throw the **** thing in the river and go buy a new genny from Harbor Freight.

[wopachop]

Do you play guitar mr Funk or maybe your buddies do? You could gently feed small guitar strings through every port you have access to. While i hate cleaning carbs ive never met one i couldnt clear to make work.

But also never disassembled an Onan carb. I have seen where small engine carbs can be cleaned over and over and over. Finally the small clog gets agitated enough to break free.

[funk-o-meter]

Thanks for the replies everyone. Looks like everybody is saying its still the carb. I may as well try a cheap knockoff and see what happens. What have I got to lose? I tried to take my rig into a Cummins/Onan service center while we where down in FLA recently but only one of 3 would even agree to look at the genny.

[185EZ]

Not sure what it costs to have one professionally cleaned but the ebay ones look identical and also are the upgraded version if you have the one with the filter that screws onto the carb.
They eliminated the filter for possible fuel leaks
Not even sure why they thought the need for 2 fuel filters

[lane_hog]

OK, don't throw away the carb....

I had the same issue -- genny would hunt and surge like crazy.

Brought the carb to a small engine shop who did a full soak in an ultrasonic cleaner from Saturday to Monday. Between the vibrating and the long soak, it's been running like new ever since.

(on edit) The cleaning cost me $30. A new carb was over $200 at the time. Now there are knock-offs that are under $70, so it might be cheaper but I'd rather have the clean original OEM carb than a knock-off which may or may not work as efficiently.

[185EZ]

Like others have said just replace the **** carb.
I **** failed to exercise my gen and the carb got gummed up
I cleaned it so you could eat off it and it still didn't **** work
And quit wasting your **** money on seafoam
I bought the cheap **** carb on ebay and it worked perfect
Even if it doesn't work it's worth the 40 **** bucks to see if it's the problem
https://www.ebay.com/itm/Carburetor-Carb-541-0765-For-Onan-5500-Grand-Marquis-Gold-generator-HGJAA-H...

[Veebyes]

Double.

[Veebyes]

In the marine world an Onan is often called an Oh No genny.

[mchero]

Good suggestions above.

What is the condition of the fuel line to the generator?
Might have a rusted pickup line on the fuel tank.

[bounder39zman]

I have attempted to clean/rebuild dozens of these carbs, with mixed results. some work great...some never quite run right. But just in case you missed this, there is a soft metal seal ring INSIDE the bowl,
that seals the bowl to the venturi tube. It is easily lost when disassembling bowl from carb. it will run like **** without it.
It will overfuel badly. Otherwise, OP's suggestions to replace the carb probably only thing to do at this point.

[wopachop]

I have some ideas and questions. If you could go back in time i would have made a temp fuel tank from a water bottle and some fuel line. Drill a hole in the cap slightly smaller than the tube and cut the bottom of the water bottle off. Use that to gravity feed brand new gasoline with a strong dose of carb cleaner. If the genny wont start remove the airbox cover and use starting fluid or brake clean. Just to see if you can make it fire up and cough out the badness. Once started the fresh fuel with carb cleaner might clear it out good enough to go camping. Will also show you if there is a fuel delivery issue.

I totally agree that removing the carb and using compressed air is ideal. Ive always wanted to invest in the little carb/jet cleaning pokie tools as well.

Im not very familiar with Onan carbs. Ive heard some people say you cant work on them. While others post about removing and cleaning them like any other small engine carb. Maybe differences in years?

Here are some questions that might help:
1. Does anyone have a link to the exploded view of his 1999 carb? I tried a quick search and found a carb but wasnt sure which model.

You mentioned there are only 2 adjustments. I wonder if the altitude adjustment screw uses a small oring and washer like you would find on say a fuel mixture screw. It seems like they are similar. If the oring deteriorated or got lost that could be why it runs bad. Or part of why it runs bad.

2. Since the engine runs decent with a load, shouldn't that point us closer towards the problem/s? The google image i saw showed a vacuum actuated choke. What if the vacuum is not working correctly with no load.....if thats even possible for some reason?

3. Have you tried running the genny and watched what the choke does during idle and then with a load? Maybe you could hold the choke wide open with your finger and see if the engine idles better after it warmed up?

4. Could also try swinging the altitude adjustment pretty far in either direction. If we think there is a slightly clogged carb passage, then it might run better if you adjust it for less air. Set it up at 8000' or whatever is highest. Thats not a fix. Just a way to get closer to finding the problem.

5. If you do the gravity feed gasoline method remember to have a catch gas for the trailer fuel line. Also without the cover on the genny it doesnt cool properly. So either run for short periods. Or setup a box fan. Just something to be aware for anyone that might read this.

Since you already removed it twice. Might be best to do it again. Not sure how easy it is to remove any plastic pieces but if you could soak the carb for days in cleaner and get a compressed air nozzle with the rubber tip you could blast out the passages pretty good. Or get a jet cleaning kit like someone mentioned above.