Re: New & need advice, questions answered etc...
The in frame two strokes are commonly known as "Happy Time" engines,or HT. All of the kits are roughly the same quality, which is "sometimes dodgy." you'll want to choose a vendor that offers a decent warranty and is responsive.
The 48 and 66 motors have the same bottom end, they just have different piston and jug. Since the actual design is for 48cc, it's rumored that those will run better, and that the 66s have more vibration troubles, that the 48s will rev higher because of this. Hard to substantiate that, but it's reasonable.