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Discussion Starter #1
Yet another tuning question from me...
My engine sounds and runs great from idle to about 3000 rpm, at which point it sounds like it is poping thru the carb - but it is very slight. By 5000 rpm it is definitly in the not cool category, and the performance drops off. This doesn't happen when accelerating (or at least it is almost unnoticable). So I'm thinking that it is running too lean(???) The plugs are whiter than I'd expect. It is currently running 68 jets in a 600 cfm holley with vaccum secondaries. The timing starts at 15 degrees, and it hits about 33 degrees at 3000 to 3200 rpm. (The damper is new, so I doubt the numbers are far off - but I don't think this noise is pinging - I can get that real easy by going up to 38 deg. total advance). The distributor is a new stock unit (rebuilt maybe). It has a pertronix.

Any thoughts, advice or recommendations? Could it be too lean? Could the feul pressure be too low? Could I have trashed this new carb when working on it?

Thanks!
 
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I haven't pulled apart a 600cfm holley in a while but does it have 68's front and rear? If if has a power valve probably around 6.5 then I would have to say I would definately jet the rears to about 74 and 70 or so in the front. Can't guarantee this is the problem but it seems to occur when the secondaries are opening. White not good, tan ok.
Is this a 302 or 351c?
 
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Thanks for the reply! I'll give the 70s a shot in front. Its on a 351C with 4v heads (so I figure it can chug some gas). It has vacuum secondaries and the softer springs seem to make the problem go away just a little.
 
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