as a rule of thumb what i've been doing for the last 20 yrs.
exhaust system is very credicule on 2 stroke glow motors
on stock mufflers use a idel bar plug best one i've used and think at one time or another i've used them all is a kb1l good all around plug if you're useing a performance pipe or muffler use a non idelbar plug os 8 a3 enya 3 also if you'r burning plugs in a motor
thats say a sport motor not a high performance engine you'r proberly running on the lean side low end or high end when you take the driver off at a idel it should drop slightly the old pinch test is a good way to check it should run for about 5 sec. before it quits thats speed up and quit if it doesn't its proberly lean. rich engines run a little sluggish lean engines burn up.

roy