the idle mixture screw is underneath the carby, the idle speed adjuster is on the side.
thing is, the idle mixture screw only affects the mixture at very small throttle openings - anywhere in the rev range.
if its running out of fuel in the top end with the throttle wide open, then its a problem with the main jet or maybe the needle. best bet is to pull the carby off and pull it apart, give it a good clean out... could be some crap in the main jet or needle jet. i would also make sure your fuel lines are not kinked or blocked either.
the best way to tell if its running rich or lean is to see the difference between the motors performance when the engine is cold and when it has warmed right up. if it runs like shit and doesnt go hard when its cold and gradually gets better after like 10 mins or so then its probably running lean. If its good off the bat straight away but then gets a little worse as the motor warms up then its rich. It will also run hotter when its lean, the exhaust might glow if its really lean and you'll just be able to tell from the heat comming off the engine. Rich mixture = runs cooler. If the mixture is right then it should be making its best power within a minute or two of starting the motor and not get worse as it warms up or on hot days.
if the bike wont idle or putt around easily with the choke off at slow speeds with only small throttle openings while the bike is still cold then you would need to try half a turn richer on the idle screw. thing is that is all it really affects, when you twist the throttle wide open you switch to the main jet.
If it was running good a week ago but isnt now then you dont need to rejet, just need to clean the carby or fuel lines out.
