Back the flathead screw out 2 full turns.  Remove the boot from your airbox to the carb so you can see the slide in the carb.  back out your thumb screw (big philips with the spring on it) until the slide stops going down.  then turn it in until the slide raises about 3mm then never touch that screw again.  after that, just adjust idle via the flathead (air/fuel mixture screw). 

Another thing to think about is your throttle cable.  Make sure it's set so that the slide is allowed to go all the way down in the carb.