Carbureted motors that won't idle below 1500 RPM are usually caused by one of two things, to rich on the idle circuits or to lean shruggy scope work
Sounds like yours is to lean twocents
Do you have another carb to try? Maybe the one you have has some internal fuel passages plug, gunk up work scope up

Mr.Cab Racing and winning with Mopars since 1964. (Old F--t, Huh)