Wow only 27mph outta an 80cc engine. My 26cc goes 30mph.It gets 200mpg. I have 4,000mile and i have only changed my drive wheel 4 times..bout 20mins of tinkering total. I like coaster brakes. Your engine probally knocking because its cheaply casted aluminum. Those engines dont last long. theres another forum. and theres a guy named fabian that swears by em. and i asked him how many miles his bike has and he says 6,000. then he says oh and i have only gone through 8 kits..lol i laughed hard and told him ya i have gone 4,000 and im on my 1st kit..hehe I dunno why they make a 80cc engine for bicycle. a bicycle is made for out put of a human about 1/8th of a horse power or 25cc. I hope you figure your kit out and have fun. I recommend you bring a tool pouch. you might need it.