you probably have your carb slide in wrong. it can go into the carb 2 ways, but only one way is right.
sounds to me like you have it in wrong, which is causing the throttle to stick.
if you take the slide out of the carb, look at it.
(the slide is the part that slides into the top of the carb where the throttle cable attaches).
you will see that the slide has 2 slots at the bottom (a short slot and a long slot).
the long slot needs to line up with the pin that's inside the carb on the side (the pin is on the right side of the carb when looking at it from above).
that long slot in the slide needs to slide down over the pin inside the carb. the short slot goes to the left side of the carb & this is where your idle screw rests. the idle screw is tapered and it lines up with this short slot on the left side. screw the idle screw in, and it raises the slide, which increases the idle rpm. screw the idle screw out & it lowers the slide, lowering the idle rpms.
either you have your slide in 180 degrees off, you have your idle screw turned all the way in, or your throttle cable is bound up causing the throttle to stick wide open.