The throttle not closing all the way with the idle stop screw removed sounds like a servo travel adjustment problem. Check to make certain that the servo is moving the linkage enough to close the throttle. Having the low speed needle set too rich will also make it hard to kill.

Too much oil will DEFINITELY make the Brison run ragged. Check your plug color. If it's black or oily colored, you have too much oil. Light brown is just right. Shades of white or grey is too litle oil. I've been running one of mine on 65-1 high quality 2 stroke racing oil for about a year now, roughly 8 gallons through it, and the piston and cylinder still look new.

My low speed needle setting is just under 1 turn open. The high speed needle is about 1-1/4 open.

One thing to note, CH Electronics suggests that the air gap at the sensor be set at .020, Brison has designed their timing ring to accept the sensor with an air gap at close to 1/8" (or 100 thousandths) on the new engines. I don't understand why Brison does this. It DOES have a very detrimental effect on the performance. It will also make it appear that you are having trouble with the ignition module. The only fix is to replace the ring with one from CH. A big pain in the butt.