Here's a post I copied some time ago that you might want to check out:
Last week I was talking with the guy I bought the 1950 B from He asked if the Ventura was loose - why yes, it is. He then told me that if it's loose it will actually rotate around in the carb while the engine's running and do all sorts of weird things. The fix - take the carb apart, remove the gasket and set the two halves of the carb back together. If the body and top fit flush then the ventura is too loose. Make a *thin* washer and fit it around the Ventura so there's a small crack between the body and top of the carb when it's put together without the gasket. When I got home I checked and sure 'nuff, the carb body and top fit together flush without the gasket in place. So, I got a piece of 18 gauge aluminum electric fence wire, made a circle, and beat it flat with a hammer - probably 0.010 or maybe 0.015 inches thick (a guess on my part). I fit this washer around the Ventura just above the 4 flanges on the bottom so the washer would be between the Ventura flanges and the top part of the carb when the Ventura was installed. I put it back together and the difference was astonishing. Now it idles down to 1050 rpm with an occasional miss and I'm sure I can get it down further with a little adjustment (my 1950 will idle smoothly down to 750 rpm without a miss - it's sweet!). The tractor even runs better at load, and the governor works like it's supposed to (before when the governor cracked open it was liable to "flood out" immediately if I wasn't careful).