Onan 5.5HGJAB-1038C

So I took a clean gear lube bottle and put some gas in it and hooked it up to the carb directly. It made no difference.

The thing was running bad today altogether without even a load on it. It started surging when it first started and then seemed to work itself out of it for a few minutes, then back to surging and finally it died. No load at all on it.

I checked to see how much gas the pump was pumping and it seems pretty weak to me. I will be changing that out for sure, but I am not confident it will solve my problem. I fear it will need to go back to the shop.

I have used Facet pumps but I think they about 4 to 6 psi. I would try to find out what the specs of your oem pump are. If the pressure is too high it may flood or run rich. It's been too long to remember all this stuff but I think some run at 3 psi or so?

There are 3 areas that could cause this. Fuel, Vacuum and governor/linkage issues.
You eliminated the orifices in the carb as a restriction. You eliminated the fuel lines and the tank. You didn't 100 % prove that it isn't fuel supply though. But on the other hand the pump "should" be able to do that and at the same time you have done a preventive repair. I have seen these pumps not last long and also seen them very old and seen cars that go 40,000 or 200,000.

So as far as vacuum, have you tried to manually slow the engine with the throttle linkage? If so was it able to stay running? Maybe not at idle but maybe close to idle?

An engine that runs at a constant speed and has a vacuum leak can start because the choke can provide a rich enough mixture. The vac leak could show up under load because it would lean the air/fuel mixture. A throttled engine could show signs at all speeds with idle being worse.

The manifold isnt loose is it? In fact I think Ive fixed onans used on lawn equipment that had loose intake manifolds.

rjxj wrote:
The fuel pump should give a steady stream of fuel. It wont spray aggressively as it's may only be 2 or 3 psi but it should give a decent volume of fuel. How about one more way to prove where the problem is? Could you connect a qt size bottle of fuel straight to the carb and squeeze feed it? If it stops surging, you have a supply issue if it doesn't change, go through the governor adjustment.

I dont know this engine but be sure to do it correctly. Small engines often use a centrifugal gear drive governor and if the internal linkage is turned too far the wrong way it can cause catastrophic damage. First be sure the linkage is in good condition. If the linkage and holes that they ride in are worn and there is too much slop it can cause surging or hunting. Another trick to prove if it's actually lean is to falsely enrichen by figuring out how to feed it just a very small amount of extra fuel as it surges.

You are running it with the air filter when it's surging aren't you? It needs the filter in the system as in theory it would give it more air (lean) without it. Some engines are more effected by this than others.

Yes, I run it with the air filter on. I just took it off to try and keep the choke butterfly closed to see if that would help.

I am almost to the point where I am going to replace the pump just to see if that is the issue. Autozone has one in stock. http://www.autozone.com/external-engine/fuel-pump?filterByKeyWord=E8016S&fromString=search&isSearchByPartNumber=true

The fuel pump should give a steady stream of fuel. It wont spray aggressively as it's may only be 2 or 3 psi but it should give a decent volume of fuel. How about one more way to prove where the problem is? Could you connect a qt size bottle of fuel straight to the carb and squeeze feed it? If it stops surging, you have a supply issue if it doesn't change, go through the governor adjustment.

I dont know this engine but be sure to do it correctly. Small engines often use a centrifugal gear drive governor and if the internal linkage is turned too far the wrong way it can cause catastrophic damage. First be sure the linkage is in good condition. If the linkage and holes that they ride in are worn and there is too much slop it can cause surging or hunting. Another trick to prove if it's actually lean is to falsely enrichen by figuring out how to feed it just a very small amount of extra fuel as it surges.

You are running it with the air filter when it's surging aren't you? It needs the filter in the system as in theory it would give it more air (lean) without it. Some engines are more effected by this than others.

Generator Jim wrote:
How about trying the cheap stuff first. Is the air filter clogged with dirt and oil that could restrict flow?.

JimL

Not an air filter issue. It does it with the air filter removed.

How about trying the cheap stuff first. Is the air filter clogged with dirt and oil that could restrict flow?.

JimL

It has an electric fuel pump, part# 149-2620. I started it up this morning and it surged a little for about the first 30-45 seconds. Then it ran great. I turned on the A/C and it ran awesome for about 2-3 minutes, then started the surging again. I held the choke butterfly closed part way and it would stay running. If I closed the choke all the way, or opened the choke all the way it would die.

It presented me with no codes at all. The light flashed a few times right when it was dying, but it didn't give me a code. I pushed the stop one time to see if it had any.

Also, I put premium gas in it that has no ethanol.

I looked at the old carb I replaced this one with and could really see no kind of air/fuel mixture adjustments. Just a plate on the top of it held on by 3 or 4 screws. I had taken that off before and the bowl when I was trying to salvage that carb trying to clean it, but I really don't remember what was under that plate.

Thanks for all the help. A guy on Fixya said this: "Timing is retarded. Check the fly wheel for any loose motion."

That wasn't very helpful to me honestly. I understand timing being retarded (but have no clue as to how to time one of these), but I don't understand how or why the flywheel could/would be loose and how that relates.

carterw65 wrote:
OK, thanks for the replies. I will check it out further as soon as I can and report back here on my findings. It could be a couple days though.

The pump seems to be working OK. Sounds like it always has. I did test it a while back and it pumped fuel pretty good. I don't have a way to pressure test it though. It is the standard Onan pump that goes on the generator. I will get the part number off of it. I saw it earlier today, but I can't remember the number.

If it is running lean, how do I adjust that? It has the altitude adjustment on it and it is almost down to 0. I am only about 800 feet above sea level.

I had to replace the choke pull off on mine. It ran but ran terrible. The only way I found it out was taking off the filter and such and watching the carb.

Does it present a code from the start switch? (light blink sequence).

Mine properly reported under-voltage, and shutdown..
it could not tell me the motor side of the generator pulley rubber had failed..

So it's a mechanical pump not an electric? If it had a high speed adjustment it would most likely be on the top center of the carb. If you were looking down on the carb the adj needle and the bowl nut would line up. Another place some carbs have a high speed adj is on the carb bowl nut.

Most newer engines have fixed jet and are not adjustable.


Have you checked the governor settings? Are any throttle linkages binding? Some throttle linkages have a long thin spring on the link itself. Each end of this spring would connect to throttle arm or gov linkage. They are used to take slop out of the linkage to prevent surging and erratic throttle shaft movement.