late or to advanced timming

have you put a vac gauge on it to see how much vac its pulling (I see you did)turn dist while watching vac gauge move it to get highest vac reading and adjust air screw to highest reading

I always set my timing and idle/mixture screws with a vac gauge to get highest reading

the poping my be from late timming after its in gear

also may want to pull a valve cover to see that all the rockers are moving the same amount and you dont have a push rod bent or punch through a rocker

maybe a lobe going on the cam of lifter cupping

what is idle rpm?

how much rpm drop does it get when droped into gear?

where is the timming set at on the damper,mine runs good at 10*-14* advanced base timing