So the 750 carb went back on, it definitely runs better. There is 2 more inches of vacuum, smoother idle, better throttle response and room for more timing without having to idle too high so it's going in the right direction. I did not reduce the jets yet, there are 70s in the front now which are stock for this model. May go down to 68s but it runs good so I'm not sure if I am going to mess with it. Has a pink pump cam in the #1 hole and a brown secondary spring, takes off great.

The reason I put the 600 on was to see if the mileage and throttle response would be better with a smaller carb but no dice, just the opposite. Like Dave mentioned in his first reply it actually ran richer, even with 65 jets. It also idled rougher and had less room for timing. Seems to defy logic a little, all the math for CFM requirements said use a 600 or less. Lesson learned.