if this is an alcohol motor a miss at high rpms will be a lean miss and it doesn't take long to melt pistons with it..can you show a pic of a plug you tune an alky motor by the burning of the thread's on the plug.and champion or NGKs usually work better for this.alky is what we raced on dirt and it cost us allot of money to learn how to tune them.....just trying to help.......Artie