If this a new carb. remove the slide an clean the debris out of the carb, any small amount will cause it to hang up. also be sure to put the slide back in correctly.
Is your throttle cable being kinked when the carburetor sets straight up? If so, reroute it so it doesn't.
As the posts above suggests, the slide, or barrel, will only work if installed correctly. There are two slots in the sides of the barrel. The short one goes to the left as you look down at the carb. The long slot to the right. It can be forced in 180 degrees out but it won't work.
Tom