6-71 BB, gas mileage

With your speed vs RPM I'm guessing you're running 3.55 gears which ain't bad for the highway but your mileage sucks bigtime there is something wrong. I'd be looking at that carb running way rich (pull your plugs and take a look at them) or your timing is completely out of wack. If you've got your vacuum advance disconnected from the dizzy hook it back up that'll help and what kind of compression are you running for this blower. Before I would go bolting on a blower I'd make sure that engine is tuned properly to the way you're running now cuss a blowers a whole new keddle of fish.