| Onan issue... [message #282698] |
Tue, 21 July 2015 12:23  |
amdgmcman
Messages: 76
Registered: April 2007
Location: Long Beach, CA
Karma: 0
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Greetings,
A couple of years ago I saw an original 6k watt Onan out of a GMC advertised with 350hrs on Craigslist and bought it, and had it installed by the gent who sold it. It starts up right waway, but soon after putting a load on it the rpms drop and it runs very rough, and then volts drop accordingly. Before I dump money into this, I'd like to know if anyone might know what the problem is. Is it tune up? If so is there anyone in Southern California that can work on it? (I really miss Duane Simmons - RIP). Thanks
AMDGMCMan
Alan M DeLuccio
78 Royale with
Coachmen,Center Kitchen Floorplan
09 Harley Davidson Street Glide
65 Corvair Monza Convertible
96 RAV4 2 door Manual 4WD
Long Beach, CA
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| Re: Onan issue... [message #282701 is a reply to message #282698] |
Tue, 21 July 2015 12:49  |
Carl S.
Messages: 4186
Registered: January 2009
Location: Tucson, AZ.
Karma: 13
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amdgmcman wrote on Tue, 21 July 2015 10:23Greetings,
A couple of years ago I saw an original 6k watt Onan out of a GMC advertised with 350hrs on Craigslist and bought it, and had it installed by the gent who sold it. It starts up right waway, but soon after putting a load on it the rpms drop and it runs very rough, and then volts drop accordingly. Before I dump money into this, I'd like to know if anyone might know what the problem is. Is it tune up? If so is there anyone in Southern California that can work on it? (I really miss Duane Simmons - RIP). Thanks
It sounds like a tuning issue to me. It could need points, plugs, and a condenser, or it could be as simple as a main jet screw adjustment on the carburetor. Depending on how long it was unused, the carb probably needs a rebuild and the gasket between it and the intake manifold might have shrunk creating a vacuum leak. If it were mine, I would put a few bucks into it. I imagine Miguel at MGM could get it going in no time.
Carl Stouffer
'75 ex Palm Beach
Tucson, AZ.
Chuck Aulgur Reaction Arm Disc Brakes, Quadrabags, 3.70 LSD final drive, Lenzi knuckles/hubs, Dodge Truck 16" X 8" front wheels, Rear American Eagles, Solar battery charging. GMCSJ and GMCMI member
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| Re: Onan issue... [message #282702 is a reply to message #282698] |
Tue, 21 July 2015 12:52 |
bobby5832708
Messages: 237
Registered: November 2006
Location: Winter Springs FL
Karma: 3
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Assuming you have not installed an electronic ignition, change the points and condenser and see what happens.
When I first bought my GMC it's Onan would run fine for 5 to 10 minutes and then slowly go downhill from there. I swore up and down it was a fuel-starvation issue but it turned out to be worn points. After changing them it ran fine for a few more years until the points again wore out. Same symptoms, ran fine for a few minutes and then started running a bit unevenly and then burping and farting until it was barely running. Let it set for an hour and repeat the process. This is the only engine I've ever seen that when the points wear out it still starts right up but after a few minutes the performance goes in the toilet.
Bob Heller
2017 Winnebago 29VE
Winter Springs FL
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| Re: Onan issue... [message #282731 is a reply to message #282698] |
Tue, 21 July 2015 20:03 |
JohnL455
Messages: 4447
Registered: October 2006
Location: Woodstock, IL
Karma: 12
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Oil the governor linkages, like Duane used to teach us to do.
John Lebetski
Woodstock, IL
77 Eleganza II
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| Re: Onan issue... [message #282732 is a reply to message #282698] |
Tue, 21 July 2015 20:05 |
JohnL455
Messages: 4447
Registered: October 2006
Location: Woodstock, IL
Karma: 12
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If that doesn't help the carb may be in the lean edge and under load can't maintain speed.
John Lebetski
Woodstock, IL
77 Eleganza II
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| Re: Onan issue... [message #282759 is a reply to message #282698] |
Tue, 21 July 2015 23:48 |
bhayes
Messages: 263
Registered: March 2010
Karma: 1
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Yes, we all miss Duane. Even though I never talked to him or met him, his contributions to keeping these old beasts running are legendary.
I'd say that getting your Onan to run reliably is worth the effort. I struggled with my Onan off and on for nearly five years, but I finally seem to have it running reliably. Here's what I did in no particular order:
* Repaired the OEM control board, which had a blown transistor. (I have a Dinosaur board as a backup.)
* Had the carburetor rebuilt by Luis Sails at Walbro. He did an excellent job and documented everything he found, and IIRC, the cost was less than $100. You can also do it yourself--just purchase the rebuild kit from Applied GMC, clean and blow out the carburetor with compressed air during the rebuild, and then set the mixture screws according to the specs and instructions in the Onan manual. Or buy a rebuilt carb from Applied.
* Checked for vacuum leaks. Check the carb to intake gasket, as well as the breather tube that attaches to the air inlet hose in front of the carburetor. The makeshift breather tube on mine was an unexpected source of a vacuum leak.
* Checked the points and condenser and readjusted as necessary.
* Checked and gapped the plugs
* Checked the plug wires and verified spark
* Lubricated the choke and governor linkages
* Verified the fuel pump was working properly and the internal filter was clean
* Changed the air filter
* Removed the fuel valve per Duane Simmons' recommendation
* Disconnected the voltage regulator per Duane Simmons' recommendation
* Changed the rubber mounts (not really a performance fix, but I did it because the old mounts were rather sad looking)
Duane's guide to resurrecting an old Onan is an excellent document to follow. And the sage advice here on GMCNET is always helpful.
If I can get my Onan running well without taking it to big guns at our local Onan dealer, then anyone can. (Okay, I'll admit, I did get a lot of advice from a seasoned Onan whisperer at our Onan dealer.)
Bryan Hayes
'76 Eleganza II
Salt Lake City, Utah
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