carb issues

Carb is 4777-2 IICR timing is all in buy 2800. Car cruises good at steady speed no matter what speed. If I accelerate at 1/2 throttle at any speed it misses no matter 90 mph or 20 mph. Push it down past 3/4 throttle and clears out and runs awesome. 750 ran good through out rpm range with stock jets 70 front 80 rear no pv in back. I just really like the throttle response of the 650 better. The 70 jets in front of 650 did help I just hope I'm not covering up a timing issue being fat like a/j said. I wont no for a little while because it - 4 this mourning and not getting much warmer soon and I have no heater. But I might get restless and get out the coveralls. Thanks so much for all your help. Ill let you know when I test things out.

Sounds like the rear main metering block machining plugs could also be leaking.