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Originally Posted by 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.
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I know it may sound stupid, but do you have a rev limiter on the car? And where is it set? I chased what I thought was a gremlin the early part of last season, changing fuel pumps, changing caps, coils, and even adding a scoop for additional carb clearance, only to find out I still had my rev limiter set at 5,600 for my stocker 400 from the prior season!
I can laugh at it now, but it was'nt funny when I was spending that Loot!
Your problem seems different than what was happening to me, but this is just my ~~>
