I have an Onan Gen Set 5000 generator in my 1994 Winnebago Class A motorhome. We were traveling last night from Michigan to North Carolina. I started the generator when we left home and it ran great for about 7 hours. I turned it off when we stopped to eat and when I went to start it back up, it would not start. When I held the start button down it chugged, blew black smoke and bounce around like it was going to come right out of the motorhome. I did this twice for about 10 seconds each. On the third time, it backfired and acted like it blew "death" out of the muffler and then it ran fine for the rest of the trip (about 7 hours). Went to start it this morning and same deal. . . but did not get it to stay started.Any help??

First thing I would check is to make sure the governor and/or choke mechanisms are not hanging up. One or the other can cause the engine to "chug" when started.

I am mechanically "special"... where would I find these?

Have you checked to see if the carburator is set on winter or summer?There is a small lever near the air cleaner.This depends on ambient air temperature to determine setting.

What happened was, you were in that period of the heat cycle where the choke had cooled off and the engine was still warm. My 95 7K Onan does the same thing. You can go out side and hold the choke open while cranking, if necessary. If you tighten the choke spring, the problem will get worse. If you loosen the choke spring, it won't start when cold. Catch 22.Richard

Richard,Thank you for the information. I tried to run it this morning after at least 10 hours of cooling off. . .it did the same thing. Any suggestions? I really need my generator!!Thanks again!

Onan Gen Set 5000 very rough start | Good Sam Community

39 Replies

martolina
Explorer
Dec 31, 2013
Where is the regulator located?
C-Leigh_Racing
Explorer
Dec 31, 2013
martolina wrote:
No. . .it will not run at all without me holding the start button

Oh yes, now we are getting somewhere.

If when you hold the start button in & it will run as long as you hold the button in, it is probably the regulator messed up or either the gen part of the genset not producing ac voltage.

The Onan genset, the ac charging part of the genset, has to produce ac voltage before the engine will continue to operate.

The gen part of the genset, where the brushes are located, the amature has two copper rings called slip rings that the two brushes contact & sometimes they can get a little corroded, so good contact between the two slip rings & the brushes can not be made, so then the gen part cant produce ac voltage.

By what you are saying, it sounds like the regulator has gone out, because if it was the slip rings, the engine wouldnt run at all because it would not be producing any ac voltage at all.

When pressing the start button, for the time you have the start button pressed in, you are bypassing the regulator & sending ac voltage directly to the circuit board, which at the time is keeping the engine running.
Neil
martolina
Explorer
Dec 30, 2013
So you disconnected the inlet side of the fuel pump and put a new hose on that end that ran into a gas tank with the seafoam mixture, correct. Do you know if there is a fuel shut-off on these units?? Thanks!
koda55
Explorer
Dec 30, 2013
When I had trouble with my generator running rough I disconnected the fuel line at the fuel pump and plug the line. Took one gallon of gas and put one can of seafoam in the gas. Hooked up a hose to the fuel pump and put the other end in the gas and seafoam mixture. I started the generator and let the mixture get in the fuel system. I shut off the generator and let it sit for about 30 minutes while hooking up the fuel line and started the generator. It has run fine ever since. I had the onan 5500 gold.
koda55
Explorer
Dec 30, 2013
When I had trouble with my generator running rough I disconnected the fuel line at the fuel pump and plug the line. Took one gallon of gas and put one can of seafaom in the gas. Hooked up a hose to the fuel pump and put the other end in the gas and seafoam mixture. I started the generator and let the mixture get in the fuel system. I shut off the generator and let it sit for about 30 minutes while hooking up the fuel line and started the generator. It has run fine ever since. I had the onan 5500 goald
martolina
Explorer
Dec 30, 2013
No. . .it will not run at all without me holding the start button
RLS7201
Explorer II
Dec 30, 2013
martolina wrote:
I am completely frustrated!!! I replaced both spark plugs, the air filter, reconnected the linkage between the diaphragm and choke, changed the oil, and it will not stay started???? Could it be the circuit board??? Don't these have issues with not staying started because of the circuit board??

Are you saying it will now start and run as long as you hold the start button in?

Richard
martolina
Explorer
Dec 30, 2013
I am completely frustrated!!! I replaced both spark plugs, the air filter, reconnected the linkage between the diaphragm and choke, changed the oil, and it will not stay started???? Could it be the circuit board??? Don't these have issues with not staying started because of the circuit board??
doxiemom11
Explorer II
Dec 29, 2013
The only time we have had a problem with ours, it was a very dirty air filter.
enblethen
Nomad
Dec 29, 2013
My 4.0 needs to be lowered to get to rear spark plug. I can get to it, but feel it is better to drop it down a little to make sure I get it out and then back in correctly.
I use a floor jack to support the pan and genset while I remove some bolts and loosen others. I takee the rear and center bolts out and Loosen the front ones. Mine needs to go down 4-6 inches to make it easier.
Have you tried some starting fluid? It may get genset to run enough to clear the cylinders.