I built a trike for a friend with a 6.5HP 196cc engine and a 20" - wheeled Mongoose trick-style bike.
It looks good, but from my experience, trikes turn nice and sharp, but they handle poorly on curves at high speed, and having a lot of power makes for a VERY SCARY ride especially if the front wheel lifts off the ground! Also being the drive wheel is on the left, the trike pulls to the right when throttling and wears the front tire funny due to the compensation to keep it riding straight.
Hopefully a 50cc chopper trike handles much better than the 196cc one I built.