OK, I'll put in my 2 cents worth. The carb may or my not be too big. It is not going to make much of a difference at idle, with the throttle plates closed (make sure they are). I agree tailor the spark curve. You need to get the centrifical advance to not change during changes in idle speed. Use an electronic distributor and change the springs to get to the point, where the timing does not change from the lowest rpm, you can keep the engine running to about 1500 rpm. I would shoot for about 12-15 degrees initial, at that rpm. thenweld the slots in the governor, to allow for about 15 degrees centrifical advance. That should be a good starting point. I also think you need more compression.