serge, sorry I just re-read your post. You said you opened up the lo speed 3 turns or.. the idle screw, and nothing changed?. If you opened the lo speed needle and nothing changed then its a fuel restriction problem from somewhere. ?? could be a pin-hole in the fuelline?.. you didnt say if the engine was new or used and how used?.. could be a small retriction in the carb, or fuel filter/pickup. Even an airleak in a gasked or crank shaft seal (althought I doubt the later). If you just moved the idle (which only moves the position of the butterfly) it wont correct a fuel issue.. Regards BobH.