Do not delete the PCV. It keeps the engine clean internally. All carbs that use PCV are designed for the air flow they add. Make sure the PCV is not gunked up. It should rattle when you shake it. If blocked with gunk, it might let in excessive air & be contributing to the problem. Have you got another one you can try?
T/slot, built into the carb, nothing there to adjust.
The o ring idea is good in concept but I think it would wear out quickly with the constant shaft movement.
This carb does sound like it has issues if 750 rpm is the lowest idle rpm you can get with speed screw backed out. Is the intake new or have you used an adapter for 1 to 2bbl?
