Reply to "engine performance"

Assuming the electronic distributor has vacuum advance, not just centrifugal, it sounds like too much carb. A vacuum secondary carb works MUCH better on near-stock engines than a racing type double-pumper. DPs really need to be set up & adjusted on a dynomometer, or they invariably run very rich & behave as you found. A 600cfm vac-sec carb will give good around-town performance and maybe 20mpg on the road, but will be restrictive at engine speeds over 6000 rpms. A 750 vac-sec carb will give 30 more horsepower with no other changes, will drop fuel mileage to around 14-16 mpg, and will allow speeds over 7000 rpm, which will probably destroy your stock engine without lots more special parts! I recommend trying to swap the 750DP for a 600(ideally) or 750 (alternatively) vacuum-secondary type carb. And add a rev-limiter to your distributor if you choose the 750!