The idle screw is adjusted for slow idle only. The idle circuit is not in play once you speed up the RPM's above slow idle and you get fuel thru the power jet.
Adjust the carburetor to the slow idle engine speed and then see how it works.
The slow idle is set with the stop screw and the idle mixture screw is to get the proper air fuel mix to make the engine run smooth at that slow RPM setting. Power jet is non adjustable.
Might be a firing order problem. This engine will run on the 1 2 4 3 order but not well. The G firing order is 1 3 4 2