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Old 11-20-2010, 08:53 PM   #1
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ONAN HGJAB 7KW CARB rebuild?

Started 2006 ONAN Gold 160 hrs after 6 months sitting. It ran perfectly for about 3 minutes then started kicking and backfired a couple of times, then ran rough and shut down. Have been troubleshooting it for 3 weeks. Called Onan tech 3 times no help. Called Robin Subaru tech 3 times tried to help but didn't. Went round and round with Just Answer.

We have eliminated everything but the carb. Everyone says carb cannot be repaired. It is running very rich. If I pinch the fuel line, just before running out of gas, the engine runs just fine. Have checked the fuel pressure, fuel flow, checked the float, needle, and seat with the pump on, all working.

I plan to make a gasket for the joint between the bowl and the main spray tube housing. Have already taken the altitude adjustment apart and plan to use that as a main jet adjustment. I have tried the engine with this needle closed and it still runs very rich.

Any help out there? Ideas welcome.

Thank you for your attention and reply,

Bill
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Old 11-20-2010, 10:17 PM   #2
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Had the same problem,and had to replace my carb.Got it for $177.00,runs great.
Tried everything to clean old carb,removed all jets and soaked in carb cleaner for a week,used air compressor blow tube and blew at every hole nook and cavity I could find.Installed carb and run for rich for 1 minute quit,check plugs fouled,like you said rich,tried that for a month,and broke down and got a new carb.What a ripoff.

http://www.partsfortechs.com/asapcar...774-p-912.html
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Old 11-21-2010, 07:39 AM   #3
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Ccook, thanks for your reply. Good to know somebody else had the same symptoms. The funny thing about this is it was actually running when it happened. One second, smooth, next second puking its guts out. Everybody blames varnish. This carb is like new inside and outside, no trace of contaminants.

I have rebuilt scores of side draft carbs, with very similar inlet systems. This carb has a gap between the bowl bottom and what would be a jet housing on a normal carb. I am going to put a gasket in there and use the altitude adjustment for a high speed mixture control jet.

Onan, Robin Subaru, and Just Answers expert blame C.A.R.B. for imposing restrictions on emission. They all say carb not fixable. I went to the C.A.R.B. site hoping to get some specs on this carb. No luck.

I say it is just a carb, and subject to the same rules of metalworking and laws of physics as anything else. Maybe I will be proven wrong. The Robin tech said they sell a short block to Onan, and Onan puts their own carb on it. Still it is a Nikki carb, and uses a very similar body to what Robin uses. Everybody says I will end up buying a carb.

Robin posts their manuals on line, including carb diagrams and parts lists. Onan sells the service manual for $18 plus $13.75 shipping and tax. I bought the manual hoping to find carb diagrams. There is one short paragraph about the carb which says, in effect, not likely to go bad, eliminate other problems before replacing. This redefines irony for me.

I read a post that said "old man Onan is probably spinning like a top in his grave".

RIPOFF is a great big understatement.
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Old 11-21-2010, 01:04 PM   #4
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UPDATE:

Right triumphs over might.

The generator is now running fine on the old (defective?) carb. I snapped the plastic altitude compensation lever off the needle. I made two washers out of a plastic water jug and put them in the bottom of the bowl.

Now the altitude needle acts as an adjustable main jet. It has a steep tapered needle, but has very fine threads. I expected it to be very sensitive to adjust, but it is not.

The trick now is to not run the main jet too lean and burn up the valves and pistons. I will now move toward obtaining or building a fuel/air analyzer for the exhaust gases, to get the mixture right.

The only thing that bothers me is not knowing what went wrong in the first place. Haven't figured that one out yet.

Bill
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Old 11-22-2010, 08:00 PM   #5
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Well I guess you did it,real good.Thats the way things are supposed to work out.Even when I was racing sports cars,I always had problems with side drafts,webers,or mikuni's the triple webers were the cats meow,but hard to tune.All the bad onan carbs around could be a relief for alot of people if you find out the problem with them.
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Old 11-22-2010, 08:20 PM   #6
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Just for grins and giggles, I would would check Wally World, NAPA, or Advanced Auto Parts for a 16oz can of SeaFoam and use 1 can for each 25gal of gas +1 extra can; ie, 75 gal tank = 4cans of SeaFoam. If your gas has caused the problem from sitting to long, the SeaFoam should clean eveything up. Be sure and drive the MH for 25-35 miles after adding.
Some info for you to read up on is contained in this link.
Sea Foam | How to Use Sea Foam Motor Treatment
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Old 11-22-2010, 09:12 PM   #7
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ccook, I cut my teeth on SUs on an MGTD, then jumped to an XKE then to a 1933 MG J2. Also have done dozens of antique outboard side drafts.

This carb had a built-in .040" gap between the bowl and the main jet housing. It went from running smooth to puking in one second. There was no trace of the necessary (missing) (non-existent) gasket. When I closed that gap, it was fixed, right now.

There is no diagram or parts for the Onan/Nikki carb, but Robin Subaru (the engine mfgr.) has a similar Nikki carb and they post their manuals on line. The parts manual does not show the necessary gasket. We have three mechanics with a total of 180 years experience scratching their heads over this one. My Just Answer Onan certified expert says he has never seen this problem. Ask Questions, Get Answers from Experts ASAP | JustAnswer You won't believe this.

We have formulated a conspiracy theory where Onan has invented a seal that dissolves in gasoline over a period of time so they can sell more carburetors. They only put this seal in one in ten carbs just to confuse us.

JC2, thanks for the tip on Sea Foam helping gas. This carb was immaculate inside, and I made a can with a tube and fed new gas into it, that did not help

I think gas stabilization is highly overrated. I just started a Kioritz weed eater on ten year old gas. I have used two and three year old gas a lot and never had trouble. I also have never had a problem which traced to old gas, where you couldn't see the evidence. That's my story and I'm sticking to it.
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Old 11-25-2010, 07:00 PM   #8
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Just managed to squeeze out the tiniest bit of information about the carburetor without any contribution on Onan's part.

The altitude adjuster is closely related to the carburetor problem I experienced. The altitude adjuster on the carb displays the patent number, 4,812,266. Looking this up in the U.S. patent database indicates that no matter where the adjuster is set, and no matter at what altitude the RV is, the adjuster is sufficiently limited so that engine damage will NOT occur.

This information is contrary to the popular assertion that if the adjustment is set at 10,000 feet and the RV is somewhat lower, i.e., at sea level, damage to the engine will occur.
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Old 11-27-2010, 07:09 PM   #9
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Keep in mind that certain Onan gensets have a known issue with the exhaust valve guide ring slipping - causing the valve to not close completely. That, in turn, causes backfiring through the carb.

The fix is a new cylinder head for about $300.00. That was my problem, documented here: http://www.irv2.com/forums/f84/onan-...arb-74526.html
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