I had the same problem with the 511 in my 69 Bee. I checked/tried everything and the hesitation was still always there. It was driving me nuts. Then I found a station near the house that sold 100% 93 octane gas. I started using that instead of the 10% ethanol crap and the hesitation went a way. May not solve your problem, but it is worth a try if you have access to 100% 92 or 93 octane.