Onan 6.5NH-RV Running Rough

[turbojimmy]

I posted this in the smokstak forums, but it can't hurt to ask the experts here, too.

1984 vintage Onan 6.5NH-RV. Came with the RV. It had sat for about 6 years when I got it. I changed the plugs and ran some sea foam through it and it's been fine for about 3 years.

Back in June while boondocking at the Pocono Raceway I needed to rely on it when my fridge stopped working on propane. It ran fine for around 10-12 hours when it began doing this:

https://youtu.be/anUuXifEvQ0

Runs rough, comes close to stalling (sometimes does stall), backfires through the exhaust occasionally.

It smells rich but there's no black smoke. Choke is pulling off just fine. I took the carb off and cleaned a piece of junk that was stuck in the needle seat. I was SURE that was the problem. Put it back together this morning and it does the same thing.

New points and condenser are on the way, but it seems like fuel?

Ideas?

[turbojimmy]

Thanks all for the replies.

I don't know what flicker points are (I'll look that up shortly) but the new points and condenser arrived over the weekend. Looks pretty standard. The carb-to-manifold gasket is back ordered, as is the top carb gasket, so I'm in a holding pattern until they arrive - target end of this week or early next week.

If the cleaning, air pressure and points/condenser don't fix it then I'll look into the ultrasonic cleaning for the carb. We just got back from our last trip for the season so it's not an urgent repair at this point. I'd like to get it done before it gets too much colder, though. It's a nice option to have when the house power goes out.

[dougrainer]

A defective condenser will cause your problem. Since you have the parts on order replace the points and condenser. Make sure you adjust the point gap correctly. You have 2 needle jets on your carb. The backside with the large wheel is the main jet and the small one on the side is the idle jet. Doug

[Generator_Jim]

You might want to check the plug wires where they attach to the coil. Over time moisture could corrode the steel wire in the plug wire. If so, carefully cut about 3/8 inch of the insulation and splay out the protruding wire. Clean the socket in the coil and reassemble. Its cheaper than buying a bunch of parts so try it first.

Jim L

[j-d]

I think you can get at the Main Jet in that carb. We had Model BFA, a twin cylinder 4KW, and I have the manual. It included certain NH models as well. That said, I shared my ONAN carb experience in another thread. It was same as Lane Hog's. Professional ultrasonic cleaning. Probably a dozen or more years ago, but a fuel system shop was able to rebuild it with new parts. Very possibly carb parts or kits are no longer available.
Anyhow, watch for any part made of copper-colored metal. Copper promotes formation of gum when in contact with gasoline. That's part of why small engines use steel lines. Yes, they can rust, but at least they don't gum like copper would.
EDIT: I remember something about those twin cylinder engines needing to be de-carbonized periodically. I never did it, and I don't recall any details beyond ONAN selling a Snake Oil for doing it.

[MEXICOWANDERER]

If your's is the model with "Flicker Points" and condenser, it would do well to thoroughly check them out. I learned through trial-and-error that the amount of fuel saved far outweighed any maintenance expense. Check the float by shaking it and invert it to double check the level. Put the inlet to your lips and make your face turn red. The tiniest seepage means it's needle and seat replacement time. Good fortune to you. Anyone who works with their hands has my respect.

[lane_hog]

Just went thru a similar saga. My solution was a small engine shop nearby giving it a three day extended soak in carb cleaner followed by an ultrasonic cleaning.

Did wonders for getting all the varnish out of the small passages that were untouchable. Runs like new.

[romore]

I use tag wire to clean the main jet and the small passages along with solvent. Make sure the tank is clean or all your effort will be for nothing, the gas will be skunky if the unit has been sitting for a long time. The coach might forgive you but the generator won't.

[Sam_Spade]

turbojimmy wrote:

Hopefully a thorough carb cleaning, points and condenser will get it back to normal. I hate to say it but the RV's value to me is diminished significantly if it has no generator.

Check the plugs too. If it was running rich they could be fouled.

And a periodic dose of a GOOD carb cleaner is a good thing to do.
If that other stuff doesn't help it, try a double dose of Berrymans B12 chemtool. If it uses fuel from the main tank, that's OK; it will be good for the big engine too.

[turbojimmy]

Took the carb back off. There's not much in the way of disassembly beyond what I had already done. Top comes off - that's about it. I blew every orifice out with 120 PSI and it's currently soaking in carb cleaner. I'll blow it out again after I rinse it off.

I had to destroy the manifold gasket removing it, so I need to wait for that to come in.

As far as maintenance goes, I'm pretty sure the previous owner didn't use the generator much, but he did maintain everything by the book (I have stacks of manuals and records for the thing). The hour meter only showed about 150 hours when I got it. I put another 50 hours on it. I changed the oil, filter and fuel filter when I first got it just in case. Most maintenance items are in 100 hour intervals.

Since it sat so long, I think there's a lot of crud in the gas tank. The fuel filter should catch it, so I can't explain the giant hunk of crud I fished out of the fuel inlet today.

Hopefully a thorough carb cleaning, points and condenser will get it back to normal. I hate to say it but the RV's value to me is diminished significantly if it has no generator.

[MEXICOWANDERER]

A carb rebuild includes complete disassembly, an overnight submergence in carburetor cleaner, a rinse in boiling hot water followed by application of a rubber tip blow gun that has 120 PSI air behind it at each and every hole visible.

Most complaints about generator malfunction can be traced to a failure to perform specified preventative maintenance operations at manufacturer's specified intervals.

[turbojimmy]

romore wrote:
Did you thoroughly clean the small passages in the carburetor and change the fuel filter?

Fuel filter is new, but I did not clean the small passages in the carb. I sprayed the bowl with carb cleaner because there was junk in there.

How do I clean the small passages in the carb? I can take it back off again - I'm getting good at it now!

[romore]

Did you thoroughly clean the small passages in the carburetor and change the fuel filter?