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Bigger piston 

IF the valve is open try turning the engine over slowly with the kick starter & watch both of the valves. if the valves don't open or close it's probably the cam chain is loose or broken. If the intake valve moves but exhaust valve doesn't close it's probably stuck from carbon either on the valve stem or a chunk between the valve and the valve seat. turn the engine over until the valve is fully open & try to clean off the stem with some carb cleaner & a Q-tip or knock the chunk out. Good luck!

Not sure how over filling the tank can make the bike hard starting. Maybe overflows into the evaporative system & back feeds the carb? Anyway take a turkey baster or a tube & pull a pint or two out of gas out of the gas tank. Put the tube deep into the tank & put your thumb on the end, to hold the gas in it, pull it out & drain the gas into something. After getting a couple of pints out of the gas tank, Hold the throttle wide open & crank the engine over for 10 to 15 seconds, or until it starts. If it doesn't start, wait a minute or two to let the starter cool down & repeat. If it doesn't start after three tries pull the plug to see if it's wet. Wet it's flooded try drying the plug with a lighter or replace it. If the plug is dry hold it against a metal part of the engine with the plug wire attached & crank the engine over to check for spark. If you have a strong white spark replace the plug & try starting the bike normally.  Hope this helps!

The "bell" OK thanks. I'm use to CVT lingo where you have a spider, spring, rollers, slides, weights & ramps.

That's why I'm running heavier weights to keep the rpm's down. A piston spinning 1 or 2 thousand times more every minute it's running is extra wear. Then take in consideration the pistons mass that has to start & stop every revolution, & that force multiplies as the speed increases. The torque of the Big Bore will do the work at a lower rpm. My wife's scooter will pull 25-30 mph up any hill in Mqt MI & that's 3-5mph better than our 2 stroke Zuma's that are probably rated higher H/P. Remember Torque does the work Horsepower sells. H/P is the speed the torque is rated at.

Unless your plug is black, wet or the electrode is deforming it can be reused. When you pull the plug it will be white if it's running lean. Go one or to jet sizes bigger. Brown or black it's rich, check you auto-by-starter/choke. Run it & see if it helps your top end, & pull the plug after you put some miles on it you're looking for a light tan when your jetting is right.

Do a search on using this forums search engine for a manual download. I was able to get one in PDF format for my wife's 2013. It's invaluable to have!!!

The bigger jet is probably where you want to be depending on the altitude you're at.
Sounds like you're very lite on the rollers from what I've read. I'm running a 72cc Big Bore with 8 gram rollers.  You probably want some where around 6 to 6.5 grams. The weight of the rollers create centrifugal force that open the sheaves/shift, less weight you need more rpm's, more weight less rpm's to create that force/for the shift to happen. Depending on the power of the engine & the load it's trying to move there's a "sweet spot"/rpm you want to be at.
Also the auto-by-starter needs power to close, Open it's in start mode constantly richening/supplying extra gas, plug it back in.
One other thing to try is if you have the stock CDI try running it & see if it helps. I've read there's some bad after market CDI's out there that don't work very well.
You can search this form for specific info say clutch/variator wieght. There's a lot of info in it. Read lots & sort through it not all of it's good info. Who knows maybe not even my info :-)