I have an '81 Passport. I put a 140cc Lifan motor in mine. it's scary fast, but fun. I tried keeping the 6v battery and lighting system, but it's kind of a pain, so I'm switching it over to 12V. The motor's 12V. Regulating it to 6 V for the battery and lighting system keeps the batt charged ok, but seems to either make a really dim or burnt-out headlight.
Couple Airhead BMWs
Couple Chinese Pitbikes