First off, 9psi is too much. Possibly overpowering the needle and seat. Try 6-7psi. Secondly, the HP carb series is more for street driving as evidenced by the 63-73 out of the box. My "other" brand 750 mech. secondary came out of the box with 76-83 which I've tuned to 81-86. Perhaps you adjusted the fuel pressure up to mask the lack of fuel delivery by the carb? You have extensions so that isn't the prob. Is all that hardware on a 350"? She's gonna' want to spin crazy rpms so you need a kick butt-dialed in fuel delivery system to keep it fed. Give us a detailed breakdown of the entire fuel system including line diameter everywhere, pump specs and location, filter size and location, cel or stock tank, etc.