She's been running great all summer till now.It developed a miss at high speed.When I checked the plugs wich are gapless type.the number one plug had aluminum deposits on it.i figured the timeing was a little advanced.I checked it and it was at 21 degreese btc which is right on .I backed it off to 19 and it still doing it .I don't know how much more I can back off the timeing.Does anyone have any ideas