Never had to worry about it before. Yes, 9901/41021 combo. I probably will need to change headers now. I didn't have anytime to practice with this motor. I was planning on club racing the weekend before with it but that's when hurricane Alex came through. Then the rain kept us from practicing this weekend also before the race. I got maybe 1/2 tank on it and raced it. I don't know if anyone has this problem, but if I'm trying to tune and there is too many other cars on the track to hear, then I have to go off of feel. Well, this being a new motor with a lot more power I ended up rich in the first qual. It all turned out good though.