Wierd Generator behavior...

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Bill and Debbie

Bill and Debbie

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Joined
Jun 7, 2014
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374
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Poulsbo, WA
I'm still pretty much a novice here but I have a question regarding my Onan 7000 generator. It seems to start and run fine. However, a few days ago I had it running in order to check the operation of the dual heaters as well as the duel A/C units.

Both heaters came on fine and blew warm...the front A/C compressor kicked on and while not terribly cold, it seemed acceptable. However, when I kicked on the rear A/C unit it lacked a bit of gusto and the generator began to run rough emitting some blackish smoke. I turned off the A/C unit and the gen continued to run rough for several minutes before clearing itself and running smoothly again.

Curious as to what was happening? And as clarification, only one unit was operating at the same time. Thanks.
 
Check to make sure the choke is fully opening. I've had an electric choke stick on an older onan before. Mine stuck earlier this year on my generac but they are completely different than an onan. On my onan the shaft was gummed up going thru the throat. Had to remove the electric coil and spray the shaft with carb cleaner.
 
92GA said:
Check to make sure the choke is fully opening. I've had an electric choke stick on an older onan before. Mine stuck earlier this year on my generac but they are completely different than an onan. On my onan the shaft was gummed up going thru the throat. Had to remove the electric coil and spray the shaft with carb cleaner.
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Think the choke is fine as the gens starts and runs fine. Something was happening when the rear AC unit was turned on resulting in the generator "loading up" and apparently running rich. Not sure what the connection between the two is...hoping someone can shed some light.
 
Is your muffler/spark arrestor clear?  Most of these you have to periodically run them under load to clean them out.  A blockage here could cause the symptoms you describe.
 
There's also a "Summer/Winter" selector switch on top of that generator, if I remember correctly. You might check its position. Our last RV had an Onan 7 Marquis and it was a pretty good generator - would power everything in the coach with no problems. Black exhaust usually means the mixture is too rich but it could also mean that a plug is breaking down under a load. You might want to pull the plugs and see how they look.

Kev
 
All great thoughts, but it was only the operation of the rear AC unit which caused the rough operation. Both furnaces and the front AC caused no issue with the generator. And each of the 4 items tested were run individually. Hence my head scratching as to what was happening when the rear AC was turned on. I presume the rear AC has an issue but not sure what.

Thanks all...
 
I'd go back to the stuck choke. When you started the rear ac the engine had to develop more power to provide that additional current. More air flow and more fuel required. If it can't get more air, the fuel is incompletely burned and you get black smoke!  I would at least try the reverse sequence (start the rear ac and then turn on the front) to ensure that it is the rear ac and not the choke.

Ernie
 
If the rear a/c has a problem, it should appear if you run the rear alone (no front a/c). Or at worst, start the rear a/c first and let it stabilize, then start the front and see what the genset does.

It's conceivable the rear is drawing excess power, but it can't be a huge amount or it would trip its breaker. Doesn't seem as though a few amps, say 18 vs the usual 12 on one a/c, would make much difference to the genset, but the total load might (spark arrester, governor, etc.). You should be able to duplicate the total laod without using the rear a/c, maybe with an electric heater (1500 watts, about same as an a/c).
 
Having to run with the choke partially closed suggestes a carb problem,, Cloggd jet to be specific.

As for A/Cs  if one seems to draw too much power.. Check the condenser coils to see if they are in need of cleaning, made a major difference on one of mine this summer, like 8 amps worth of difference (or more)
 
william, the 18 hours you speak of in your sig line, is that total life of the generator? or just since you bought it?

If it has only ran an hour a year for the last 20 years, that maybe your problem. generally speaking on this forum it is recommend to run it about 30 minutes a month at at least 50% capacity or about 30 hours a year. So that generator should have at least 600 hours on it.

As for the issue you are having. can you duplicate it? I understand that you used only one item at a time, this also may not be enough of a work out for the generator. you should be able to fire everything at once and even microwave a pizza pocket.

My advise is to try again to see if it was a one time occurrence as in a bit of dirt stuck somewhere. If it does it again then follow the other trouble shooting steps and check linkages etc on the generator.
When was the fuel and air filters last replaced?
 
Actually the gen was thoroughly tuned up prior to our purchase including oil, filter and plugs. Could start a little easier but has always purred well the times we have run it including a couple of two hour runs. The roughness only occurred when the rear AC unit was fired up....and the AC was laboring. I'm thinking it needs looked at. We've put 1500 miles on the coach since purchase and it's been solid.




 
If you converter was putting a bulk charge on your batteries, two electric heaters, one air conditioner,, and the surge from starting the second would certainly load down a 7k gen set.
 
Actually the gen was thoroughly tuned up prior to our purchase including oil, filter and plugs.
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That's good, but it doesn't address the potential for a clogged carburetor. When a small gas engine sits for long periods, the fuel often evaporates in the carb and leaves a varnish on the tiny passages inside, restricting the gasoline flow and altering the air/fuel ratio. That can cause hard starting, rough idle, and failure under load. It is a common problem with gas generators and one of the key reasons why regular genset exercise (30-60 minutes at 50% load, monthly) is receommended.
 
Gary RV Roamer said:
That's good, but it doesn't address the potential for a clogged carburetor. When a small gas engine sits for long periods, the fuel often evaporates in the carb and leaves a varnish on the tiny passages inside, restricting the gasoline flow and altering the air/fuel ratio. That can cause hard starting, rough idle, and failure under load. It is a common problem with gas generators and one of the key reasons why regular genset exercise (30-60 minutes at 50% load, monthly) is receommended.
Click to expand...

Thanks Gary and all. Wondering if a bit of Seafoam could be sucked through the carb to clean things up a bit?
 
It could, but if you feel comfortable enough to remove and disassemble the carb would be better. When we pulled my buddies carb a part it had a lot of sediments in it. The carb cleaner  won't remove that. It may how ever remove some of the varnish, if it has it.
 
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