4hp stage 2 might be a hype because the porting is faulty there which might cause it to be worse than the stock (however this may not be true, but that is what some users reported). I wish I had my old engine to compare to to know if the stage 2 kit (with stock porting) really is worse or better than the stock 1 piece cylinder kit. When ported, then it will produce the true power. Porting is fairly easy to do, just need patience.
But then again there is another pocket bike engine builder in this forum and he claimed that his stage 2 runs better and stronger than his stock 1 piece cylinder pocket bike engine that he compared it to. So don't get turned down. I myself would rather not port it because I have no experience with that and will just admit that the stage 2 kit has more power than the stock cylinder kit.
You can read up pocket bike planet if you do not agree, and I am not pro at this so that place can help.
For me I don't mind either and am happy with the stage 2 kit as long as it has a lot of power (which can be hand ported easily to gain more power) because the way the stock cylinder sounds is ridiculous and loud.
By the way, what RPMs have you reached?