At loss... what next?

Try this: carefully and one at a time pull the spark wires (I usually take notes when doing this kind of troubleshooting), then put the engine BRIEFLY under load. Do this with each cylinder in turn, one at a time.

As you put the tractor under load, you should notice a marked difference in performance with one spark wire disconnected, UNLESS it is cutting out on the same cylinder every time AND that cylinder is the one with the spark wire disconnected at the time the engine DOESN'T seem to run worse.

If you find one cylinder that doesn't seem to make much of a differnce whether it is disconnected or not, you've at least isolated the problem to that cylinder, and probably also ruled out a fuel system problem (except maybe cracked manifold, bad manifold gasket, etc.).

There is also the possibility that the venturi itself is defective and causeing a vacuum to be in the bowl area of the carburetor. Try removing the high speed needle completely. If that fixes it you can be assured there is a problem with the venturi. Lots of the later venturis are plastic and we all know what time does to plastic.

Zane

• Hobby farm