Half turn to the left? [:-] That sounds VERY lean to me.

Tighten all the way in and give it 2 full turns out, then start, place the throttle in the middle, if it sputters and dies tighten haft turn and try again.

Keep tightening 2-3 clicks at a time untill the engine does not sputter on half throttle, then apply full throttle and tighten SLOWLY untill peak RPM.

Once you got the max RPM un-tighten it 3 clicks.

That should be a somewhat safe setting

Joe