Been lurking awhile, posted a bit on Moped Riders Assoc. a while back (2012) Not much activity there.
So...I'm 57, retired, and have a 1981 Yamaha QT 50 since brand new still in GREAT shape. In 2012 I gave it an all Yamaha 60cc top end (no longer available from Yamaha) PW50 gears, orange clutch springs, and IRC 77 tires. Still on stock carb and rear bored out muffler.
I can do 35 mph I think, can't top speed test where I live, my road has big potholes and on a ridge top so I don't like going steep downhill to get to flatter areas. Also bike is not correctly titled. My Dad signed it over to me without a notary before he died and I still have to try to get through the red tape to make it mine.
I've read about doing compression tests on these engines that regular long hose testers give low readings. True?? I'm getting 90 PSI on mine.
So how are the 60CC Niche kits REALLY? I have a YT60 head I'm using for cooling. I'd just use the cylinder, piston, rings, etc.
I also have had a line of motorcycles through the years, currently a 2015 Yamaha FJ-09.
I wish this forum had sections by bike type. Also when you post, always put bike type in it. Shows up in searches that way.
I hope to help here, have wrenched on my own bikes for years and also was an automotive tech. way back.