I use engines from bicycle engines.com, they advertise them as 80 cc's but they are actually US 66 cc's, and have well enough power they are 2.9 HP. It's a good company with people you can actually talk to on the phone in the US if you have a problem. The quality on kits from Amazon, e bay etc for $100 are scetchy. You need a steel frame bike with a 36 spoke pattern, aluminum wont take the vibration of a 2 stroke. These are not for everyone, and you need a little experience with gas motors, but they will get you where you are going and will cruise at 30 MPH ( they will hit high 30's but you are pushing that speed for a bicycle). The do make 100 cc kits if you want to get nuts with speed. There are a lot of youtube vids on installation and set-up, a decent bike and kit you will have $500-$600 into.
