I am working on a fresh mild 440 in a 69 Coronet RT 4 speed. It has a new Thunder Series AVS 800cfm carb. It performs super except for a very slight tip in bog or pop back throught the carb. (lean?) under VERY light acceleration at about 1000RPM. Moderate throttle or harder it is not there. It is NOT the secondaries.

I have the accel pump in the closest (rich) hole. I have richened it one jet and about as far as I can with metering rods on the low speed side. I have the springs in it to move the metering rod sooner (pink). It has helped, but I cannot completely eliminate the sag. Any ideas?

THANKS.