custom motorized bike

hey i found a old bike that could fit a small engine on it so i got one went to my buddys house and put some forks and handlbar brakes but wen i was useing the bike i broke the plastic stuff in the throttle grip so i was trying to thing of maybe other ways of useing the throttle like the brake or if there was a metal made throttle grip id think that b good but for the bike just use it to cruise around toronto so if anyone knows any laws about them id like to no