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Discussion Starter #1
I have an Onan engine 20 hp Performer XTS that the carb was rebuilt and new intake manifold install with new gaskets. Ran fine for about eight hours and now I got it back in the shop with the same problem....surging. It will run fine as long ads you dont engage the mower the it will start surging. shut the deck off and ring it down to idle then slowly back upto wo throttle and it tuns fine. Any assitance will be helpful. Thanks for taking the time to answer this thread.

Ernie
 

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I had somewhat of a similar problem on mine and tracked it down to the diaphragm on my fuel pump,I'm not saying it's your problem but replacing mine worked for me.my engine is an 18 HP is an 18 HP onan and I don't know how similar they are
 

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If carb is all set correctly, then possibly water in fuel. The Onan carbs seem far easier for foreign particles in fuel to set them to surging. Both my Massey & my friends Case 446 start that surging once or twice a year. Always a particle of crud in the main jet. Your newer carb may not have adjustments on the jets like the old carbs. Anything at all in the jets will do this....be it a particle or even thin film of varnish, as you can't simply open the main jet screw to compensate. Sometimes it can be as simple as a weak governor spring. When carb was worked on, are you sure spring was put back into same hole on governor arm?
 

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Discussion Starter #4
Yes it was, And thge carb was soaked 3 days again and a new kit. It has a idle jet screw and the carb was blown out. I believe that it's the manifold. I sprayed some cab cleaner while it was running mid range and it started surging. Just at a lost. Never have had any problems with Onan till this old wheel Horse came into my shop.
 

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Yes it was, And thge carb was soaked 3 days again and a new kit. It has a idle jet screw and the carb was blown out. I believe that it's the manifold. I sprayed some cab cleaner while it was running mid range and it started surging. Just at a lost. Never have had any problems with Onan till this old wheel Horse came into my shop.
Where did you spray it?in the carb.or around it and on intake gaskets.How old is the tractor?Mine has two adj.screws,fuel and idle.Maybe too much fuel,or gov.out of adjustment.
 

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Discussion Starter #7
It's a 3 peice manifold. Split length wise and I sprayed along the split. They usesilicne to seal it and I believe that it was to little. I am going to check the spring tension to make sure that base is covered.
 

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Discussion Starter #8
Was this the one you bought a NOS intake for? I still have that used intake.

Yes olcowhand. It really bums me out as I try never to get a machine back with the same **** problem... How much for the intake u have.
 

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It's a 3 peice manifold. Split length wise and I sprayed along the split. They usesilicne to seal it and I believe that it was to little. I am going to check the spring tension to make sure that base is covered.
1st problem I see is that silicone was used. Gasoline WILL disolve silicone. Never-ever use it between the carb and heads or vacuum leaks may / will occur. Ask me how I know....... I learned the hard way.
 

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Discussion Starter #11
The silicone was factory. This is a brand new in the box manifold. The split manifold was in my opine a big mistake.

Well by noon or later the epoxy should be cured so I can reinstall the manifold and find out if it cured the problem.
 

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Like I said in your other post, I used motoseal white and little bolts. Now they only seem to sell motoseal gray.

I think they changed the name of motoseal white to this product so car people will use it also. Same package.

If you read the info it's states manfold gaskets. I used it on a onan intake a few years back and have had no problems.

Most silicone don't hold up to gas but this one seems to work.

Good for next time maybe ?

http://www.permatex.com/products/Automotive/automotive_gasketing/gasket_sealants/auto_Permatex_Form-A-Gasket_No_1_Sealant.htm
 

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Discussion Starter #13
Well I got in from the shop about 11:00 and the Onan's surge has abated to about 40% of what it was. Still I will notlet this unit back out untill it is completely repaired. Now it is a slow surge instead of the rapid up and down. I adjusted the spring with no apparent difference,

I am at wits end.
 

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At this point, I would take the main jet out & use a torch tip cleaner to slightly enlarge it....and I mean very slightly. I've had that problem before on non-adjustable carbs and it solved the problem. Actually, I believe the plug over the main jet is the same thread as the older carbs had with adjustable mains. You might find an old carb & swap this all out.
 

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Discussion Starter #15
Thanks olcowhand. I may have access to a carb .
 

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Discussion Starter #16
Up date. I did as olcowhand said and it cured the problem....

Thanks olcowhand for the tip...

Thanks to all for the advice as it was a learning lesson on this Onan.
 
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