My 68 GTO 400, 4 barrel has a new thumper cam 475 lift. I am having trouble with the carb idle mixture. First of all my vaccuum reads 8 at idle and 18 when driving correctly, then 0 when I stand on it. It read 12 at idle before cam change. I have searched for a vaccuum leak and have not found one. It smells very rich and surges at off idle (1600 rpm). I tried to adjust my idle mixtures and they did not respond, I took them all the way out and no change in idle. ANY IDEAS? I'm lost.