I’ve been chasing a lean condition and not sure the best way to fix it. I’ve got a 750 DP with a Proform main body and Holley metering blocks. #74 in the primaries with a 6.5 PV and #84 with no PV in the secondaries. The motor idles at about 1100 rpm with 9-10” at 14 afr. Cruising at 55 mph at 2600 rpm the afr is about 13.5. WOT the afr is about 12.5-13. The problem area is part throttle about 1/3 to 1/2 throttle it goes really lean, about 16-17 and you can hear it miss. It happens when pulling away from a stop or accelerating to pass on the highway.
I’d love to get a Sniper EFI but that is a ways down the road for me.
How did you come up with a 6.5 power valve? that's way too late of an opening. You need to measure CRUISE vacuum and set the power valve to that. Everyone tries to cover a tip in issue with accelerator pump and transfer slot. But when you open the power valve that late, you get tip in issues.
Never set power valve opening by idle vacuum. That is wrong. Set your cruise A/F ratio with the primary main jet. Then control tip in and WOT with power valve opening and power valve channel restriction. Once you have your cruise A/F ratio set, never set WOT with the primary main jet. Use the PVCR and lean or fatten up WOT with that and your secondary main jets.
I think you are a bit fat at cruise. I'd like to see a plug or two. I'd bet you can lean out the mains a bit more and the fix the tip in and WOT with power valve tuning.
Again, do not set PV opening from idle vacuum. I know Holley still teaches that, and they are still wrong.
