[red78ta]

Around 5200 it starts to break up & backfire through the carb. My combo should be good to 6500 but will be happy with 6000. Have tried numerous timming setting & advance curves including locking out the advance totally. Only slight changes in reaction but still present. Doesn't matter hot or cold. Seems like a timming issue but am running out of ideas on where to look. Getting VERY frustrated ......... could this be a valve float issue even though the cam spec says valve float should not occur till 7200? fresh built 400 (about 2500mi. now) stock crank & rods, cast pistons, bored 30 over, 6x-4 heads shaved for 9.5:1 comp.(this is a street/strip car), Crane cam (P/N 284281) adv duration 296/304 (234/242 @ .050 tappet) with 473/488 lift, stock 1.5 rockers, Valve adj. to 0 lash w/Polly locks, Tomahawk intake, holly 4150 750 cfm carb. & Pertronix HEI.