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.
Cruising at 2,600RPM, it is likely that you are on the main circuit. And I agree that 13.5 is a bit rich for cruise. Smaller main jets will probably bring that mix down, but could exaggerate the lean transition problem. In order to fix the lean transition, you have to know which circuit is the culprit. It could be the slots, it could be the power valve, or it could be the emulsions or the bleeds delaying the mains. Sorry to make it complicated but you have to know what is wrong before you know what to fix, let alone how to fix it.
You may use a timing light shining into the carb and try to duplicate the lean spike to see if the mains are in at that point. As a starting point, it would be important to know if the boosters are engaged or not at the point of the lean spike. If they are, then the power valve or PVCRs would be where I would look as you are on the main circuit at that point. If not, then I would look to bringing the mains in sooner and/or fattening up the slots.
