Check n° 1 : the tip of your screw is broken off and still in the carb body.
Try to blow it out with compressed air.
Check n°2: intake air leakage, check manifold with brake cleaner spray while in idle mode. When idling goes up in RPM, there's a leak.
But your engine needs to be tuned correct first, valves/timing/etc
1954 Oval L275 (in progressive refinement)