I haven't tried one yet but I intend to get my next engine from Dax. The two cycles are your best bet for power to weight. However I have found with the chinese kits that I have spent a bit replacing the kit parts with parts of more "reliable" manufacture. Such as the clutch handle. I also find I am replacing parts on the cheap chinese Huffy I started with so keep that in mind as you begin your project. The hook with these things is that once you start you are always looking for ways to make it better! Don't expect to get away with just $150! I speak from experience!
If it can't be broken I'll find a way!
I'm not lost, I'm exploring!