JD3010 gas MS USx21 Accelerator pump diaphram AR10108

Getting hard to find this repair part, when you do it costs a fortune $60. I can't seem to keep this part working, when it leaks your tractor won't idle. Has anyone disabled this diaphragm with gasket material or a beer can aluminum? I see they want a $1000 bucks for a new redesigned zenith, but only use the tractor for pushing snow in the winter. Any help appreciated to get this old work horse running well again.

I gave up on mine years ago ! Got lucky and found a good used Zenith for a really good price. Ours is a 4020 but the carb. was from a 3020 ? It had an adjustable load needle added and seems to work fine. This might help widen your search to find one from another model.

If you want to try blocking it off, all that would be needed is to find the vacuum passage that operates it and block it off. It could be tapped for a small screw or allen head setscrew.

But I doubt you'd like the way it would perform without the accelerator pump.

Drink a beer and cut out two strips. Use them to block both passageways, the upper and lower on the back cover. Have done this many years ago to my 4010 gasser and it works fine. If you move the throttle open instead of yanking it open it won't stumble. If you yank, it may or may not stumble depending on conditions i.e. if the engine is warm. Like you, I got tired of fighting it.

My experience with my "67 3020 is similar. It ran but in a very poor manner and fell on his face requiring choke to keep from dying and yet still smoked at idle. Grrrrr.

When I took it all apart I found both the ball check valve and the spring on the discharge (engine side) of the accelerator pump missing. On the fuel bowl side that ball too was missing.

These ball checks HAVE to be there and the one that is spring loaded MUST have enough spring pressure to hold the fuel back under the operating vacuum or it becomes an open passageway dumping fuel (without any air) like a small soda straw.

Anything wrong with these checks, spring or the small keeper blade (depending on model) will make your tractor rather unfriendly! After replacing the check balls & spring as well as the $60 dollar diaphraghm (though mine did notleak it was hard as a tombstone) it behaves quite nicely. I found it to be picky about fuel mix adjustments. A very little twist of the idle mix screw is the difference between smooth flawless behavior without smoke and hesition faltering as the governor opens the throttle.

It demands full choke to start and as much as 1/3rd to 1/2 for a while once started until it gets some heat in there.

I see many giving these MS carbs the thumbs down and experience shows me they"re touchy with their adjustments. I"ve however found mine to behave quite well once it was all there & adjusted. I"ve worked on Zenith carbs too and admit they are more forgiving but I"m finally quite satisfied with my USX.

The tractor in general I found to be unforgiving of its formerly missing thermosat! Proper operating temp made a big difference!

Good luck.

I do appreciate all the helpful suggestions from this board and the many people who have tinkered with these Marvel USx carbs. My old JD 3010 gasser has been through the war and back again including being hatched by too much starting fluid by some past owner! I still think it carries a bent camshaft, the timing marks are crazy... yet the old tractor runs amazing well when the USX when the Accelerator diaphragm is fixed. Oh yeah, its been a yearly ritual to put in a cheap set of Champion plugs which look terrible after a winters snow plowing. I've learned to talk nice to old Johnny..may this tractor live forever! Thanks again!

On a cold start mine had immediate coolant flow in the top tank of the radiator. I purchased a thermostat before I even opened it up. There was none in there at all. With a system flush, new T-stat, new coolant (60% water) it needed a bit more adjustment, especially idle. Now his Champion D21 plugs stay handily clean.