ive got a 306,carbureted with a holley street avenger 675cfm. its got a .512 lift comp cam dual pattern. at 5200rpm the motor experiences severe "valve float" or what i thought it to be. ive changed the valve springs to accomodate a .550 lift. ive replaced the distributor as well to an msd unit. ive also changed the msd 6al out as well. ive even put 1.6 roller rockers. still no change. im out of ideas. could my cam be too radical for stock lifters and make them collapse under load or is my carb too big?? any ideas??