Thermoquad idle issue

crewchief said

This 1972 340 block and heads sat in the basement since the mid 80's. I built it from the bottom up with all new internals, crank, rods and pistons last year. Block was bored 40 over standard machine work was done. No deck cutting and heads were machined for new valves 2.02. Stock intake was not cut either just checked for cracks and squared.
Hydraulic Flat Tappet Comp Cam 260H, duration 260/260, Lift .440/.440 with 901-16 spring kit.
Cam break in when perfectly, high zinc, drained after 30 min run. Engine ran better during break in then now. Rings should be set with 500 mi on the motor.

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intake not cut, but squared? not familiar with term squared. what does that mean?
when I used to do heads, I checked each port with vacuum to make sure each valve makes perfect seal with seat. In the past, Ive found heads cut with the form cutters, ie Serdi, et al, can be cut off valve stem c/l or out of plane. I don't know why, could be inadequate setup, poor procedures, worn machine or tooling, whatever, but I've found poor sealing issues on several occasions with professionally done heads. If you were close, I'd remove the carb, and rockers and check vacuum at the carb mounting surface. If that proved bad, I'd remove the intake and check all the intake ports for vacuum, too.
By the way, have you checked intake manifold bolt torque, since break-in?