Carburetor idle mixture screw doesn't have any effect?

I'm trying to adjust my carburetor on my 50cc 2-stroke Yamaha Aerox but when adjusting the idle mixture screw I'm not noticing any changes. I read somewhere that it should increase your engine's rpm's at idle when adjusting in the right direction but when I do it nothing happens. The same amount of smoke. Same rpm's. Same sound. Same everything.

I have cleaned the carburetor thoroughly already so that shouldn't be the issue.

Could it just be that the screw is having an effect on the engine but it's just very difficult to notice without any special equipment? If so how do I know when the screw is adjusted correctly?

 

The problem could be you slide is set too high and the engine isnt ticking over on the idle circuit.