IMO, I would sell that carburetor and go to the Thunder 650. That carburetor you have now is an AFB style and is far inferior to the AVS style. The AFB has the secondary air door below the secondary boosters. The AVS secondary door is above the boosters. This allows much more of an accurate signal to the boosters and allows for a much smoother transition into the secondaries and allows for greater adjustability. All of that, plus the extra 50 CFM and you'll be right on top of what you need for that engine, IMO. Others may disagree and say you can run a 750. You probably can but it will require more tuning to get it right, IMO with that gear you have. I think the 650 Thunder AVS is a perfect match.