Clean or replace the jets when in doubt.

Take a pic of the slide.  It sounds like it’s sticking from being worn/rough.  Take a pic so we can see how bad it looks.

If you flip the carb upside down, the slide won’t necessarily open completely.  The spring won’t compress enough for it to completely open.  If the slide won’t move at all when flipped upside down, it’s sticking.  It should at least move a little and clack around on the idle screw.  Be gently clacking it around.  The spring compression shouldn’t be strong enough to hold the slide completely closed.

Note: the spring acts more to help close the slide after you’ve rolled off the throttle.  It offers a little resistance when rolling on the throttle.  Most of the slide action is vacuum-driven (thus CV carb).