People do NOT want to hear this, but almost ALL vacuum carbs DO NOT OPen all the way, On the dyno. a double pumper will alway make 15 to 25 MORE HP since the vacuum carb is not openong fully. If your are still fouling plugs, the heat range is TOO COLD for your type of driving. You should get the HOTTEST heat range you can find, and MAYBE, you will get thru this, It is all going to come down to your carburetor. SOMETHING is WRONG with it. You should replace it with a known carb that works well on another engine.

JOE SHERMAN RACING ENGINES