Henry's 70 Dart Swinger

whoa man-sorry I didn't see this earlier!

Are you running your old AVS, or the new Edelbrock? As far as the sizing, a 650 is about perfect for a stock 340-the cfm calculators are a little bit flawed in my opinion. It's more about the tuning than the size. Even a 750 double pumper can be tuned to run well on a stock mildly cammed 340.

If you're flooding at low rpms and it's bogging out, you might consider trying a weaker step up spring under the rods-if you're not pulling enough idle vacuum, the boosters will dump gas into the barrels and make it run super rich.

If you can get your idle down to <1000 rpm, how much vacuum does it pull?