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Adjustment of marvel-schebler carburator

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james rekus

06-22-2000 18:07:10




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After rebuilding the carb on my WD, the engine runs like it is starved for gas. sometimes belches & sputters. I've re-adjusted float height. Idle jet adjustment seems to have no effect on engine idle. Full load adjustment seems to have no effect after about 2 or 2-1/2 turns out. I ruined the paper bowl gasket, so made one of cork. It is about 2 or 3 times the thickness of the paper one. What effect on engine performance could this have? Does the venturi have to fit snugly with both the upper & lower parts of the carb body?

Suggestions appreciated. Jim

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brian(pa)

06-23-2000 09:12:08




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 Re: adjustment of marvel-schebler carburator in reply to james rekus, 06-22-2000 18:07:10  
make your gasket out of a cereal box it's close to the thickness of the original gasket.



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Dick L

06-22-2000 20:34:38




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 Re: adjustment of marvel-schebler carburator in reply to james rekus, 06-22-2000 18:07:10  

I have never put a thick gasket in a carb, but it would put the discharge jet in a different position in relationship to the orfice in the throut. I am not sure what the effect would be. You should get the proper thickness gasket. Are you sure that you have the proper gas flow from the tank? 2 to 2 1/2 turns is where you start on the full load setting. You cant fine tune this setting untill you have the tractor under full load, ( Dyno or disk, drag, plow, or something to that will pull the engine down. The idle adjustment screw is actualy the fuel air mixture adjustment. Turning the screw in shuts off air and makes the engine run richer. Turning the screw out adds air to the mixture and makes the engine run more lean. You start this adjustment at 2 turns out, start the engine and idle the engine as much as you can and still keep it running, then turn the idle screw in untill the engine starts to slow, then slowly turn the screw out and the engine will speed up some and continue to turn the screw out slowly untill the engine just starts to slow, at this point if your RPM's are at the proper idle speed you have completed the idle adjustment. If your engine is not at idle, the idle adjustment screw will have no effect when turning it in or out. At half thorttle you can take the screw all the way out. That is one of the reasons it is refered to as an idle screw.

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Brian G.

06-24-2000 17:52:44




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 Re: Re: adjustment of marvel-schebler carburator in reply to Dick L, 06-22-2000 20:34:38  
I'm quite sure that turning the screws out (both the high speed & low speed jets) richens the mixture by allowing more gasoline into the circuit. Gasket material is a relatively cheap item. I always keep an assortment of thicknesses available for situations like Jim is dealing with.



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james rekus

06-25-2000 08:37:19




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 Re: Re: Re: adjustment of marvel-schebler carburator in reply to Brian G., 06-24-2000 17:52:44  
Thanks to all who replied on the carb adjustment. After getting the correct bowl gasket & re-checking all adjustments a third time, I dediced the carb was not the culprit. Out of desperation I installed new points & condenser and it solved the problem. The way my engine was running I would have "sworn" it was the carb.

Another lesson learned. Jim



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