Since this is your first YS, make sure you did not connect the lines backward. Another word, make sure the check valve is in the pressure line (left side of the engine when viewed from rear) and that the check valve is facing in the right direction. Use a fuel filter between the engine and the check valve to prevent crud from clogging up the check valve. Use another fuel filter in the feed line between the tank and the engine. I had four YS .63's, and none of them backfired or threw a prop on me. You should be fine if you are not running your .63 too lean. The regulator screw is there for you to tune your midrange. If you slowly advance to half throttle and the engine begins to load up, then you are too rich on the midrange. Turn the regulator screw clockwise 1/8 of a turn at a time until the engine stops loading up. On another hand, if you slowly go to half throttle and the engine begins to detonate, then you are too lean on the midrange. Turn the regulator screw out 1/8 of a turn at at time. I get great results with Powermaster YS 20/20 fuel.