on my 78 pa50II that isn't even close to prime condition and is all stock. I put a pollini replica pipe from treats on the other day and it went from barley getting up to 27 mph on flats to easily 38 with waaaaaay much more mid and top end power and acceleration (low end still sucks but I got a 70 cc kit coming in the mail tomorrow hopefully)
Check out the treats hq store and get some aftermarket in my opinion those Japanese know how to do alot of things and mopeds is one of them.