Onan generator running rough

[John Stephens]

Since buying my coach 3-? years ago, I have religiously exercised my Onan 5500 generator every two weeks under half load, just as the manufacturer suggests. I change the oil every 150 hours, the air filter every 300 hours, and when it had 450 hours, I had the plugs replaced. It now has close to 980 hours and has run very well for me.

For the past two months, my coach has been in the shop having several repairs done and waiting for a new awning from Dometic. I was assured by the service advisor that they would exercise the generator as needed while they had the coach in their shop. When the shop owner realized it was going to be another month before getting another awning after discovering the one that had been sent was defective, I told him I needed to take the coach home so I could do a few repairs of my own before the end of the month when I return to work.

When I picked up the coach, it took over 30 seconds of cranking before the generator would start, and when it did, it ran like it was missing a cylinder, spewing black smoke out the exhaust. I checked the hour meter and found it to be the same as when I dropped the coach off. They had not exercised it as promised and it sat there for two months. I had not used a fuel stabilizer before dropping it off because I didn't think it would be there for that long.

I have started the generator at least four times since getting the coach home. Each time, it acts the same, black smoke and running very rough for the first two or three minutes or until I put it under load by turning on the a/c. Then, it smooths out and runs as it should.

My question is should this be something to be concerned about? It runs well after it gets going, but quite rough until then. I wonder if the carb needs to be rebuilt in the event gas lacquered in the bowl. Should I get the carb rebuilt? I don't have the expertise to do it myself and am hoping that since it runs all right after a couple of minutes that I may be able to get by for another couple hundred hours before taking the thing into the shop. Since it has close to 1,000 hours on it, I'm wondering if it may need more than just the carb to be worked on. It has performed very well up until now.

 

[Gary RV_Wizard]

It's not likely that the carb "lacquered" in just two month of non-use, but it is conceivable.  However, a gummed up carb doesn't start running better after awhile, so I would be looking elsewhere. A sticking choke would be my first thought. The black smoke indicates a bad air/fuel mixture, but if that clears up as the engine warms that probably means it is a temporaty problem. The choke is the gadget that helps a cold engine by adjusting (making "rich") the air/fuel mixture until it warms up.

 

[darsben]

Sticking choke
Elevation adjustment  set wrong on bottom of carburetor.
Gummed up carburetor
in that order.

The extra cranking time is probably because the gas all drained back into the main tank

 

[John Stephens]

Thanks guys. A sticking choke or an elevation adjustment is a lot easier and cheaper to fix than rebuilding the carb. I know where the elevation adjustment is and can get to it myself. Where is the choke and how can I fix it if it is sticking? I know on the old cars with carbs, we just used carb cleaner to keep it from sticking. Is this the same?

 

[darsben]

Thanks guys. A sticking choke or an elevation adjustment is a lot easier and cheaper to fix than rebuilding the carb. I know where the elevation adjustment is and can get to it myself. Where is the choke and how can I fix it if it is sticking? I know on the old cars with carbs, we just used carb cleaner to keep it from sticking. Is this the same?

The same remove air cleaner and while engine is running spray carb cleaner into carb as well as exterior of area.
P.S usually you cannot rebuild the carb has to be  replacement as no service parts are available for some.

 

[SpencerPJ]

John: I Googled, and there are many videos on cleaning the carb, I was not sure of your year or exact model.  Seems like old school cleaning with Gumout.  I am a fan of a product called SeaFoam, it's a great gas system cleaner.  Also, does it have a fuel filter,  partially blocked filter can cause all sorts of grief.