Help me get the off-idle stumble out of my QF 750-AN Double Pumper

I would also recomend you check the ignition is set and working correctly (mechanical and vacuum advance, etc).
Also this article is worth reading on how to setup the idle on your carb. About 2/3 down the page it mentions the correct butterfly position to have for a smooth transition from the idle circuit to the main circuit.
http://www.circletrack.com/techarticles/ctrp_0707_carburetor_tuning/viewall.html