To check for air leak you can also use carb spray around the intake boots,head,bottom of cylinders to see if it starts reving up higher.also look at a carb diagram for a stok set and find the air screw..turn it all the way in,then back it out 1in a half turns.do it to both sides.Sounds like you may have alot of carbon build up on the pistons as well,they will keep running even if you unplug the wires , there is to much carbon built up..good luck..JB