Make sure the carburetor is closed against the idle stop when the trigger is at the neutral position (finger off trigger) and the servo trim is centered at zero. If this is how your linkage is setup, then the idle gap is too wide and that needs to be adjusted.

Many mixture changes requiring going richer or leaner is done with the mixture needles. Idle gap is adjusted by the screw on the back of the carb that goes in at an angle. The high speed mixture is on the fuel inlet stem and the idle mixture needle is in the end of the throttle valve (carb slide).