i put one of those kits on my bike (chinese 80cc really means 66cc), pic related is mine
pretty fun, i got mine up to 32mph with a 180lb rider. they will, however, make you smell like 2 stroke oil (positive or negative depending on your outlook tbh)
mine crapped out after about 3 months. i might get a 4 stroke kit if i do another. less noise and stink
check out
sickbikeparts.com, they have a kit that allows you to use the rear gears on the bike as well as some performance exhaust pipes for the 2 stroke ones
