I have been building PW's for a lot of years. I dyno my stuff. But the dyno does not always translate to real world power but very close. I get motors in from all over the states. I get requests for two kinds of motors... 1, Fast and can't tell that it is modded. 2, Fast and we don't care if it looks modded.
I see tons of money being put in these bikes for no reason. People will pay for a bore job for 60cc and porting and head work.
The proper way to do it is to replace the whole top end with the STOCK 60cc three wheeler top end. (two more ports). Cylinder, head, piston all bolts right on. That bigger cylinder has more vacuum and just about evens its self out with the stock 50cc jetting. The air screw can do wonders on these, almost like an adjustable main jet. With the 60cc top end there is naturally more power and much more RPM which equals more top end speed.
I have seen many good porting jobs but more bad ones, making things almost impossible to jet.
I have seen these bolt on 60cc cylinders ( with the stock 50cc head and with the stock 60cc head ) last for years of pounding.
Even when using the stock 50cc head on the 60cc three wheeler cylinder there is very seldom an over heating issue.
I have clocked my PW's at 50mph ( useing the tall tires) with only the top end swap from the 60cc three wheeler.
This was using a 36 tooth drive gear ( yes they are interchangeable) . 33 is stock, 34, 35 and 36 will also fit if you can find them.
Recently in the stock classes people use the 34 tooth because it can't be spotted nearly as easy as the 36 tooth.
There is a misconception that gearing down gives a better hole shot, fact of the matter is that the PW50s take X amount of time to wind out, it would have to be geared to the moon in order to make the hole shot slower.
In a stock class a 34 tooth will out hole shot a stock 33 tooth 99% of the time. And always have a better top speed.
On the very fast PWs I have learned how to get an extra inch of travel from the front end, it doesn't sound like much but when you have almost zero travel to start with it makes a difference in controllable top speed. Tall, fat almost non motocross tires work as well or better than regular MX tires. Tall street semi-knob (scooter tires) work the best, give you ground clearance and all the traction you will need plus the much needed extra suspension.
I have a track and a gate, and PWs that I have built, I have found that the aftermarket clutch springs don't help at all, waste of money.
I leave the oil pumps on, I sometimes put a dab of oil in the gas. With more RPM's from the 60cc 3 wheeler top end, there is more fuel and more oil from the pump. It evens itself out pretty well.
I hope this answered some questions.