Coming to the party late. I got a 408 stroker engine from Blueprint that came with a 750 VS carb. The engine ran OK except for low speed where it was very lazy. Plugs after just a few minutes of running were black, pig rich. Could not put a vacuum gauge on it to adjust the idle mixture because the gauge needle was going crazy because of the valve overlap. Long story short: Changed the power valve in the carb from 6.5 to 4.5 and that cleaned everything up. Very responsive at low speed now. May even test going to a 3.5 at some point.
