Hey guys! Well I put a Lifan 120cc engine in my 73 Z50 and I was very impressed with the power and speed. The only problem I do have is the tranny skips 2nd when down shifting sometimes(skips in N). Guys on Evil-bay are selling new Lifan engines with a bore and stroke of 55mm (bore) 59.2mm (stroke). Does that make the engine a true 140cc? I've been told that the 138cc engines are 124cc? Also, the new engines are an all up shift pattern. This seems better to me. Has anyone had any luck with this new engine? I'm planning on putting the engine in a 1971 CT70. What type of HP and top speed do you think I can get from the 140cc engine? I have my little Z50 geared for top speed with the 120cc engine and it does 55mph(8 inch wheels, sea level and 175lbs rider). Do you think I can get 65mph with 140cc engine and 10 inch wheels? Any help will help. Thanks for looking.