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Old 11-25-2018, 10:06 AM
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street avenger issues

My 408 big block chevy is 9.67 to 1 with factory big oval port 101cc chamber heads. I have a 270 magnum cam in it and a weiand stealth dual plane intake plus super comp. headers and 2 1/2 inch exhaust. I have a Holley 770 street avenger carb on it. It had a terrible stumble when you crack the throttle at most any speed. I mostly fixed this with a bigger pump shooter. However at speed if I just tip into the throttle it immediately starts to misfire unless a fair amount of throttle is given. I have put at least a hundred miles on the new plugs but can't get a reading on them. They look as new as the day they were installed. I have 70 jets in the primaries. Could it be too lean? I don't have an A/F guage at this time. I have about 13" of vacuum at idle and 18" at speed. I tried an 8.5 powervalve and it gave too much fuel too early. The 6.5 seems to work the best. I checked timing and for vacuum leaks and all seems well. I tried ported vacuum and found manifold vacuum gave the best results for the spark. Does anyone have a jetting recommendation?
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