strange engine issue from 900-1400 rpm

[Clavo106]

ok my friend.my 2 cents.. if its engine in searching at idel i would looking for a Frist vac leak. then timing... now iv never rebuild a q jet but I have rebuilt plenty of motorcrafts... I few years a go I had similar experiences with a friends of Cadillac he bought a eldbroc carb and slap it on left it seting for a few years and ask me to get it running.. I got it fired up thru it in drive ran for a bit then died. when I thru it in reverse admittedly died.. I did everything . look and adjust timing about more time I could count sprark. vac leaks spark. coil dis.... and how many time I adjust the A/F screws a bout a hundred time it did not change a thing.... I finely gav in and told him if he had the original carb he said he did.. so I slap that bad boy on and worked solid. drove great.. not saying it would work for u but im thing looking at that carb another time would not hurt.. good luck..