There are a couple of things you can do... First, don't tighten the top of the carb with a wrench, (only hand tight!) Over tightening it can warp the carb body & cause the slider to stick.
The same kinda goes for the clamp that holds the carb onto the manifold, cranking that as tight as you can could warp the carb body also.
If you have to leave it a hair loose for the slider to not stick, the carb might come off the manifold while riding, in which case you can put a small sheet metal screw through the side of the carb into manifold to hold it in place.
Also, make sure the carb cable doesn't have any sharp turns or 'kinks' in it that can hold the carb open, (& no tight zip-ties holding it to the frame.)