I had a B on my 230 in my 64, & got 16.5-18.5mph. I kept it under 65 mph, stock w/HEI w/34 degrees total advance, Taylor plug wires(try them, I was amazed), 3.73 gears & 3 speed & light foot. But I had it apart about 4-5 times before I was satisfied the power valve was not sticking-polishing it & the bore w/000 steel wool did the trick. brian
