When I tighten up the idle screw on the carburetor way tight (almost all the way in), motorcycle zooms forward?

You probably have confused the idle stop with the mixture screw or if this is a slide stop that's what happens. You are akin to a monkey bashing an engine with a stick. You both have tools but no idea how to use them. Hopefully you haven't ruined the seat in the carb by bashing your screwdriver against it. Look up how to adjust a carburetor or visit a mechanic.