Remove the carb and muffler.

First inspect the muffler pressure fitting and make sure it is clear.

Insert a small hex key to clear it.

Next check the muffler nipples as well, you may have debris in there.

Pull out and check the needle valves and make sure that you have not put "rings" into the smoothly tapered seats.

Clean everything.

Once done, put a piece of new and clean fuel tubing on the carb inlet nipple and blow as you move the throttle open and close.

With it fully open you should get a very pronounced "HISS" out of the carb as you do so.
When you fully close the throttle, you should NOT be able to blow into the tubing.

Turn the HS needle in gently. You should be able to reach the point where you CANNOT blow into the carb even with the throttle fully open.

Turn it back out, and check to make sure that the amount of air changes as you turn it out.