Onan Gen Set 5000 very rough start

Richard,

One other question please?? There is a metal fuel line running from the fuel filter down to the fuel pump. I am thinking since I am tinkering I would go ahead and change the fuel pump and filter. . .can that metal fuel line be replaced with a flexible black tubing? Thanks again!

Richard,

I figured there was supposed to be something holding that linkage in place. Does the choke/diaphragm self regulate if it is working properly? Should I use some carb cleaner while I have it opened up?
Thanks again for your help!!

-Marty

I have a 2001 Onan 5500 in an '02 Georgetown. I had cardiac surgery just before Christmas 2011 and didn't get to the "exercise" routine for 4 months. The SOB hasn't run since. It's not a big deal for us as we're FHU site people, but I guess I'll have to get it fixed before we try to sell the rig.

Since it only had 48 hours on the Hobbs meter after 8 years with the original owners when we bought it, I guess they didn't use it much either! It has about 60 hours on it now.

Martolina wrote:
Richard,

Wow. . .thanks for the details. I went out this morning and looked at it closely in the light. The link between the choke and the diaphragm came off?? I reattached it, but still no luck with starting. Should there be a nut or something holding that linkage between the choke and diaphragm or should the pressure between the two hold it in place? As long as I hold the start button in, it will chug. The diaphragm makes a "air sucking" sound when I pull in and out on the lever. Can that diaphragm be changed without a whole lot of hassle?? I pulled the air intake off the carb and when I hit the start button, it had little "spits" of gas coming out of the choke hole?? Could the fuel pump still be bad? Again, thanks for all of your help!!!

OK, you've found the problem. The linkage is held on the slotted lever with a very small washer and a "damn-it clip". (damn-it, I dropped or lost another one). You can use a small cotter key or maybe a small paper clip to hold it in place. Look closely, there is a hole drilled across the end of the linkage.
Because the choke pull-off has not been working, the engine is extremely flooded. You will need to push the top of the slotted lever to the left as far as possible, while holding in the start button. That will allow the engine to clear its self and fire up. Stand clear of the wet black exhaust, or your laundry person will be up-set.

I just noticed you have the air cleaner off. You could stick a soft object (led pencil?) in the carb and prop the choke plate open instead of holding the lever to the left.


Richard

martolina wrote:
C-Leigh Racing,

Thanks very much!! How hard do you think it would be to replace the fuel pump?

Why do you think it would run fine for hours and then start being stupid?

Thanks again!

By your last reply, sounds like you have several problems & all could be fuel & carb related.

Normally on a small engine, which is what most Onan gen sets are, spitting back out through the carb, can sometimes be a stuck valve or to lean of a mixture in the cylinder & being sparked off before the valve closes, but not always.

The choke rod you found loose, there should have been a type of clip holding it, to keep it connected to the vacumm pot & there should be a short hose connected to that vacumm pot leading back to the intake manifold, where it will get its operating pulse from.
A gummed up carb, can cause the float not to swing/move freely or can cause the inlet needle to stick open/closed or half way open. That in turn, can cause the engine to flood with fuel & blow black smoke out the exhaust.
If the needle should be stuck half open, the engine could very well run & blow black smoke out the exhaust & then after some time of running like that & heat building up, start to running correctly or almost correctly.

An Onan gen set, most are old school type engines, valve in block type & will just about drive you crazy with all the different things can go wrong with them. It is something just built into them. The newer models with valves in the heads, do away with a lot of the old model problems, but are more high tech with computers & such.
Why in the world the RV industry has stuck with Onan I have no idea. With all the different things an RV owner has to deal with, seaming like just before your about to pull out on a trip, why not put a quality Honda gen set in them & do away with some the crazy problems we are having to deal with.
In my years of small engine repair, 95% of the repairs I had to make on small engines, was fuel related problems & only the other 5% left was a failure of a moving part.
This gas we have had to deal with, for "years" is not worth the time it would take us to drive to a station & bring a jug full home, but we are paying for high quality.

You probably need everything checked that has anything to do with fuel, from the fuel hose mounted to the gas tank, all the way up to the carb.
Another thing, you asked about the fuel pump, it is located on the back side of the gen set behind the gen part of the gen set. The starter motor is also located back there as well, so with either one you'll need to pull the gen set out of the compartment to access either.
Neil

Richard,

Wow. . .thanks for the details. I went out this morning and looked at it closely in the light. The link between the choke and the diaphragm came off?? I reattached it, but still no luck with starting. Should there be a nut or something holding that linkage between the choke and diaphragm or should the pressure between the two hold it in place? As long as I hold the start button in, it will chug. The diaphragm makes a "air sucking" sound when I pull in and out on the lever. Can that diaphragm be changed without a whole lot of hassle?? I pulled the air intake off the carb and when I hit the start button, it had little "spits" of gas coming out of the choke hole?? Could the fuel pump still be bad? Again, thanks for all of your help!!!

The black smoke on start up indicates too much fuel, so bad fuel pump, bad fuel filter or gummed up carb is not the problem. You indicate that it runs OK once it gets past the start up issue, so it could be a sticky choke shaft or a bad choke pull off diaphragm. If you can locate the choke pull off diaphragm, you can remove the hose attached to it and attach a longer hose and suck on it to see if it holds a vacuum. The choke pull off diaphragm will have a bent wire hooked to it that goes to a slotted lever. That slotted lever attaches to the choke shaft. Check to see if the choke shaft is free to move in its bore. Let us know if you find the answer.

Richard

I have been looking at this in the dark. . .where can I find the choke. . .is it behind the Carb. on this model (onan Gen Set 5000)

C-Leigh Racing,

Thanks very much!! How hard do you think it would be to replace the fuel pump?

Why do you think it would run fine for hours and then start being stupid?

Thanks again!

Yuo could try starting your gen without the air filter black smoke means low air flow or stuck or mis-adjusted choke