they make a very nice 155Z motor with 1/4 the HP more than the 140cc. and there are tons of upgrade parts for it to turn it later into a 180cc engine if you wished. the 140 can only by upgraded to a 150cc. so i do recommend the 155XZ motor. www.tboltusa.com sells a nice setup complete with carb and harness. We use them a lot for parts in the 4-stroke side of the house.