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Open Roads Forum  >  Tech Issues

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

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maillemaker

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Posted: 09/09/19 08:09am Link  |  Quote  |  Print  |  Notify Moderator

Here is a great forum with detailed repair manuals for rebuilding carbs and more:

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

Mechanic in a bottle solutions seldom work with gummed up carbs. As others noted there are tiny passages in the carb that must be manually cleaned with tiny brass wires or other means (being careful no to damage the orifices!).

Also I recommend you clean the slip rings if the genny has sat a long time.

This is why it is critical to run these gensets every month, and let them run for a half an hour under load so that the heat and vibration can help agitate the fuel inside the carb and help keep it clean inside.

These things do not tolerate sitting well at all.


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wopachop

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Posted: 09/09/19 12:55pm Link  |  Quote  |  Print  |  Notify Moderator

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.

bounder39zman

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Posted: 09/09/19 06:26pm Link  |  Quote  |  Print  |  Notify Moderator

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.

mchero

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Posted: 09/09/19 08:22pm Link  |  Quote  |  Print  |  Notify Moderator

Good suggestions above.

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


Robert McHenry
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Veebyes

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Posted: 09/10/19 09:44am Link  |  Quote  |  Print  |  Notify Moderator

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


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Veebyes

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Posted: 09/10/19 09:44am Link  |  Quote  |  Print  |  Notify Moderator

Double.

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Posted: 09/10/19 08:05pm Link  |  Quote  |  Print  |  Notify Moderator

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........712089654cb76a38469746de8acaad675c6e7a34

* This post was edited 09/10/19 08:14pm by 185EZ *

lane hog

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Posted: 09/11/19 06:01am Link  |  Quote  |  Print  |  Notify Moderator

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.

* This post was edited 09/12/19 02:34am by lane hog *



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185EZ

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Posted: 09/11/19 01:37pm Link  |  Quote  |  Print  |  Notify Moderator

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

funk-o-meter

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Posted: 09/28/19 05:47pm Link  |  Quote  |  Print  |  Notify Moderator

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.

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