You might want to pull the button off your motor and check where the plug is supposed to be. If it is too short it will not fire right at idle. Very difficult to tune. Too long and you know what will happen.
Make sure what ever plug you use goes to just about flush in the bottom of your button. Don't let it protrude into the firing chamber and don't let it be short of the hole. This will get the best burn for ya and make the motor easy to tune.
OS makes long plugs as well.
TEX