Re: KTM-50 RPM Killer or Predator 212cc Torque Monster?
Maybe try a 49cc pocket bike engine if you want more power within the legal displacement limit if its 50cc. You can get ones built with all the tuning parts turnkey. It'll be like a Morini, albeit a couple less HP, and only cost about $150. I wouldn't mess around with a 99cc engine or a 212 if it is the difference between you being deported or not. If you want torque for hills a 49cc four stroke with gears would be plenty reliable and fast. I agree with you on China girl engines, it's really a shame about the reliability since they are so easy to hook up. I've been playing with the idea of getting another china girl kit for a kick around bike, but I know it would end up consuming too much time keeping it running.
Four stroke is better for reliability, if you can find a small water or oil cooled engine even better. 50cc Lifan autos fit on chopper bikes. You can use traditional tuning to make more power on popular four strokes, like cam, porting, compression, lightening, a simple 1000W generator engine could probably be tuned up to about 3hp. Centrifugal clutches are good for small engines, as are CVT's for keeping in the power band. Pocket bike CVT's are cheap on Ebay. If you want a bike that is practical for everyday I would go with the best engine you can afford, something Honda or cloned is a good choice.
KTM50 Schwinn Chopper - 6000W E-Motard - 52cc Auger BMX - 9sp+CVT 52cc Cagllari Moped