Hi big kountry 75,
We specialize in building American made drive systems, and use the 49 CC four stroke HS 142A motor in our kits. The HS 142A motor has proven to be a great motor for motorbike use because of its wide RPM range [2000 to 8000 RPMs] and durability. The Honda GXH50 is an optional motor for our kit. Our drive has been attached to a wide selection of 4 stroke motors, and one of the recent choices has been the Harbor Freight 79 and 99 CC motors.
I would suggest email or PM me to discuss prices and options, as we don't want to break any rules on this site.
Have fun,