Generator Problem

Hey Everyone,
I have a 1987 Travel Master with an Onan 6.5 NHE Genset. When we first got the RV about 4-5 years ago, the genset didn't even work. Broke one of our own rules and bought a RV without a working generator. Try to make it a short story.
It runs but it can only run one major appliance at a time. We can run one of the air conditioning units with the microwave but it really bogs down. Try to run the other AC unit with the other and it kills the genset. I put a volt & frequency meter on it and at idle it's running 129v and 60Hz. Turn on one AC unit and the volts drop down to about 115v. Can't remember the exact Hz but it's somewhere around 55-57Hz. Try putting on a bigger load and it just bogs down even further. Tried to adjust the governor but I can put the throttle to the "floor" and the rpm's, volts, Hz, they don't increase. The fuel line is hard as a rock so I'm going to replace that all the way back to the tank in case there is a crack letting air in somewhere. But what else could it be?
Here's a list of things that I have replaced on it since we got it:
rebuilt the carb then tuned it
fuel pump
air filter
control board
bridge rectifier
emptied fuel tank, poured 6-8 bottles of carb cleaner and let it sit, poured in 5 gals gas, ran it through & filled the tank with fresh gas (it has it's own fuel tank)
plugs
ignition coil
converted to electronic ignition
the hour meter doesn't work but it reads 250hrs. the genset has never ran for very long so we have probably put 5hrs on ourselves

Any help would be greatly appreciated.
Thanks,
John

Hi John,
Sounds like you are already pretty knowledgeable about the genset so I am going to avoid the pat answers one usually gets to these questions.  Did you actually rebuild the carb or just do a cleaning?  Not a lot of people rebuild these but quite a few try cleaning with mixed results.  If it is not responding to ?throttle to the floor? I would lean toward it being misadjusted and running too rich.  Giving a rich carb more gas can make it bog down as it try?s too flood.  Or it has internal passages that could not be cleaned.  If you can find a replacement carb it might be worth the money.  If you cleaned the carb please tell us how you did it.  Someone may have a better method.
Good luck!

At first I thought you'd missed plugs but no.. You got 'em.

After sitting for years the carb could be gummed up beyond the chemicals you have used and may need a proper dissection and cleaning and reassembly.. Other than major overhaul that's about all I can think of.. Check compression as well (The major)

THe slip rings may also be tarnished limiting current... Not sure how easy to clean

x? on the carb also stop by an electric motor shop and purchase a "com stone" undoubtedly the commutator is dire need of a cleaning.

I had a similar problem on my Onan in my Winnebago. Went through the same troubleshooting as you did, along with cleaning the Carb. Did not help so I bit the bullet and bought a new Carb and that fixed the problem.

John From Detroit said:

THe slip rings may also be tarnished limiting current... Not sure how easy to clean

Click to expand...

Slip rings and probably replace the brushes not too hard and most likely a kit available usually use a fine stone on the slip rings and fine grit sandpaper to seat the brushes.

Thank You All
Looking back in my records (usually pretty good at keeping them, usually) we have owned it 4 years and I believe I tackled the carb cleaning, (I thought I had got a rebuild kit but can't find any record of it so I must have just cleaned it) shortly after getting the rv. Cleaning, I took it apart as far as I could and used the spray carb cleaner.  I would also imagine I would have used a pipe cleaner if it would fit in the passages. I'm fairly ocd about cleaning these type of things. Pretty sure I let the parts soak and then blew it out with compressed air. If I'm going to take the time to take it apart, I will typically take the time to clean it as best as I can.
No doubt the brushes could need replacing, but it's only a volt issue because the gen engine can't throttle up.  At this point I'm going to finish the fuel hose replacement but don't have high hopes of it fixing the issue. I'm also going to look into what it would cost for a carb replacement and see if it is doable for me. If not, I will try an actual rebuild and cleaning.
I know what the brushes are but what are the slip rings that were mentioned? Is that what the brushes are set up against? Also, what is the commutator?

Thank you all very much!
John

When I replaced my carb been about 6 years it was right around $100 and was not that hard to change. What I remember the only hard to get to screw was in the back bottom rear.

You mentioned converting to electronic ignition, did you set the timing correct? If the engine can't rev, it's either timing or fuel related. 

Normally most small generators are set at about 62-63 Hz at no load so when they load up they will drop to around 60.

DItR said:

.
I know what the brushes are but what are the slip rings that were mentioned? Is that what the brushes are set up against? Also, what is the commutator?

Click to expand...

Yes slip rings are the metal parts the brushes ride against.
A commutator is like a slip ring in a DC generator.

John,

Most Onan carburetors are of the same basic design and I've been into a few. Mostly the same passages with different sizes. After cleaning, rinsing in water and blowing dry,I like to run a bristle off of a wire brush through the small passages. Hows that for OCD? I find the needle seat assy to be the most problematic. Most that I've worked on have non-replaceable seats. I like to take a new drill bit of the appropriate size, to keep it square in the bore, and burnish the seat by hand. Shoot for about 0.030 polished area. The needle will drop down in the seat and will be sealing on a fresh surface of the needle. Set the float to level with the carb body and give it a try. Adjust main jet to lean roll and then adjust to rich until lean roll goes away. Then readjust under load.
If you are satisfied with the tune, then maybe the engine had carbon build-up. Carbon build-up = higher compression which leads to detonation under heavy load, which causes power loss.
Dumping water and various chemicals into the carburetor to clean out the carbon is a waste of time. Mechanical removal of carbon with a wire brush is best. I'll bet you own a torque wrench.

Good luck

Charlie, yup, I set the timing. The guy I bought the Onan kit from had made some great instructions to go with it. He even called me before he sent it to walk me through the procedure to make sure I understood it all. Great guy.
Richard, your ocd beats mine, you win. ? I called the Cummins/Onan dealer that serves my region & they cant get a new carb, its discontinued, & couldn't find one that supersedes it. Looking online the cheapest new carb I could find was $255. Expensive little boogers. But I might have to bite the bullet & get one. I'll have to debate that in my head vs a rebuild kit & extensive cleaning. The time to do that may be too much to tackle that at this time. I have many more irons in the fire.
I got the fuel line switched out & I readjusted the main jet. The Onan manual has two different settings for the main jet. One has you turning the main jet out 1 1/4 turns out from seated. Different section has 2 1/4 turns from seated. I had it with the latter. Last night I readjusted it to the former & it seemed to run fine. I'm going to hook up my meter today & test it.
Thanks for all the help. I'll let you know how it goes today.
John

1 turn on the main is a lot. A rich engine has less power and more heat than a lean one, unless it is too lean. Was it sooting the plugs?

Put the meter on it. Have not tried adjusting the governor yet.
At no load its putting out 135v & 65Hz. With one AC unit going it drops down to about 122 + - & 61Hz + -. Turn on 2nd AC unit it drops to about 115v & 58Hz. (I can actually turn on the 2nd AC unit & it doesn't kill the genset. Yea!) With both AC units on I can turn on the microwave & I think it dropped down to about 110v. Cant remember Hz. But it wasn't steady power. You could see the light in the microwave fluctuating. Can turn one of the AC units to just blower & it does ok. I can live with that. It just seems the governor isn't quite compensating like I would expect it to, but again I haven't touched it yet.
To this point, I put in the new fuel line & fuel filter, readjusted the main jet to run leaner, & cleaned the spark plugs & all that seemed to help alot. Hey, got 2 AC's to run at the same time. That has NEVER happened. Now I will try tweaking the governor to see if I can get it to work properly.
Anymore suggestions are still greatly appreciated.
John
P.S. The plugs didn't look the same. One was black & the other more gray. Thoughts?

If one side has an intake leak it would be leaner causing a lighter plug read. Shut off all loads and  manually slow the engine down with the throttle linkage  to see if it will stays running at a low speed. Sometimes intake system leaks can be pinpointed with something like wd 40 etc. I have used starting fluid but that's more dangerous method. If it draws the wd40 in you will hear a change in  the engine speed or smoothness.

If you can keep the engine at a consistent slow speed use a pair of insulated spark plug wire pliers to remove one plug wire at a time and listen for differences in what each cylinder is contributing.  It may well stall but it may stall easier on one side than the other. You are looking for differences from side to side.

Thanks Q, I will try that. Nice trick. I also heard somewhere that a bad plug wire could also cause the black plug. I've never changed the wires & I believe they may be original. Still have the Onan green on them. I think I'll start with the wire & if that doesn't fix it then I'll look at the intake.
Thanks again,
John

Im no mechanic, and I dont know when Onan started putting the adjuster on the gennys for altitude, but any chance you are at a higher elevation then the coach was previously and the setting needs changed. If yours doesnt have one, Im out to lunch. Heres a link to what Im talking about. The explaination is at the four minute mark. https://www.youtube.com/watch?v=kBQ4uIGhmkE