Your bike screams for a straight pipe It would sound good on a 4 stroke might even go to a larger dia. could sound like a mini hog. I want to some day get one of these 4 strokes and play with the timing and look into making a different cam. I start slobering of thinking what could be possible with a engine like this. Nice bike.
Norman

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norms-iron-works.tripod.com
motor assisted bicycle engine headlights that work off of your white power wire. check it out