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Holley 670 0-83670 Tuning Help

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  • Holley 670 0-83670 Tuning Help

    I have a mildly built Ford 400 (9.3:1 compression, roller cam and rockers, headers) with a Holley 670 0-83670 Street Avenger carb. I'm running a mechanical fuel pump and the carb is about 8 years old.

    I just got my AEM AFR gauge hooked up and I've been tuning the car. It originally had 68 primary jets and 76 secondary. It was running rich with this setup, both at cruise and at WOT. I dropped the primaries to 67, and the AFR is pretty darn close to 14.7 under most lower speed cruising. Once the engine gets to about 2700 RPM, the cruise mixture enriches to closer to averaging about 13.5, but the AFR also starts to fluctuate way more. The lower speed cruise has a much more steady AFR. So I'm not sure if this is caused by the power valve starting to open, or maybe the fuel curve of this carb?

    Dropping to a 74 secondary jets has my AFR in the around 12 or so at WOT, so I'm probably still a bit rich there. David Vizard says 13.2 is ideal for power, so maybe 72s would work better?

    I also tried 66 primary jets and it ran about 15 or so when at lower speed cruise, and my faster cruise was in the 14s. Vizard says 15 or so is ideal for cruise, however, I seemed to also get a bit of light detonation under very heavy throttle at times. My fuel is a bit old so that might be part of the issue.

    I noticed another issue cropped up. The engine won't start hot if I just turn the key, even with an immediate shut off and restart. I now have to give it a shot of gas first (pump the pedal once), then it starts fine. I never had this issue before, it would always restart hot okay if within 15 minutes or so.

    Any advice is appreciated, as I'm not as experienced as a lot of you on this forum.