u throttle shaft

jr1983 · Oct 17, 2014

The throttle shaft on my u is free and moves like it should with
the tractor off. When I start the tractor it freezes up and wont
move. I can force it by hand but it sticks at about half throttle
band wont move at all unless I force it by hand. Has anyone
ever had a symptom like this? I have rebuilt a few hundred
carburetor in my life and this is a new one on me.

T.R.K. · Oct 17, 2014

2 things come to mind:

1. loose throttle plate on the shaft, (Or upside down or backwards).

2. extremely worn holes/shaft allowing the throttle plate to actually drag on the bore.

O.K.: the third thing:

A gasket or other debris blocking the travel of the throttle plate.

Alan K · Oct 17, 2014

Have you checked the governor?

jr1983 · Oct 18, 2014

The throttle shaft is new. I will pull the carb off today and make sure the butterfly is on right and free of debris. The govornor I think is working fine. If you uncool the linkage and control the the throttle shaft by hand it binds up and is barely moveable.

Earl-IL · Oct 23, 2014

A little warping in the manifold or carb. flange & too thick of a gasket or over tightening of the carb bolts will lock up a throttle shaft. Has the carb been bored for a larger throttle plate ?

Alan K · Oct 23, 2014

The only other thing I can think of is if there is a burr on the body of the carburetor that is binding on the throttle shaft or too tight of a seal on the shaft. I have had that on one I redid.

jr1983 · Oct 23, 2014

The carb has not been bored but it took every trick in the book to attempt to save this carb. It soaked in carb cleaner for two days and soaked in evapo-rust for another day to open the passages up.the manifold is a multi-fuel recast. It is about two years old. Bought it new. It is the type you turn the muffler to divert the exauste. I dont know exactly how tight it should be but I think I used a wrench and a pair of pliers to put it on. Not proper I know. I think it is freezing up. The top of the carb and the bottom of the intake frost up. It seems when it melts after I shut the tractor off it loosens back up. Any ideas?

Earl-IL · Oct 23, 2014

You may have to polish the coated throttle shaft a little. Look for burrs. Ream your bushings??? I find a lot of new throttle shafts that are not straight. When they machine the shaft for the throttle plate it lets the shaft distort a little. I put them in my lathe & check them. Does your intake have a 1/8 pipe plug where you can check the vacuum . Normal is 17-20 in. If it is running high you might try a larger venturi. a lot of tractor pulling engines has this problem of frosting . Some people wrap the intake above the carb with high performance header insulation. Start it & let it warm up, shut it off and let the heat from the engine transfer to the manifold.

u throttle shaft

jr1983

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T.R.K.

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Alan K

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jr1983

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Earl-IL

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Alan K

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jr1983

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Earl-IL

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