I have a couple things to say. One, you put a predator on that bike, its a motorcycle. two, cops are going to notice an engine that big and you wont be able to tell them its under 50cc, whether they tear it down to check or not. you will get pulled over I guarantee it. just out of curiosity, what 14 year old needs a motorbike powerful enough to be considered a motorcycle? i know that some teens are experienced off road riders, and thats a different story. but how bad could you need transportation to consider spending $400 to 500 on building a motorized bicycle, when you could build a complete bike with a two stroke engine for less than around 300 or less? with a predator engine, you are going to need a gearbox and motor mount, and those are not cheap. not to mention a mb is going to be a challenge if you are not mechanically experienced. you can get a two stroke kit for around 160. i got my bike at walmart for 75. thats 235, and my bike has held up for two years just fine.