pros- low gearing, reeds, decently fast stock, small
cons- wheel base is short= very nimble but scary at speed, can't re gear, as you already stated little performance parts.
small preformance run down in order of power, mph ,and easiness.
take off the oil injector and premix gave me 3-5 mph and a little more power-free
expainsion chamber needs to be welded on unless if you get a simo. which has a high power band and most people don't like it. unfortunately the simo is out of stock on treats, who was the only person with them. i wleded up a biturbo and got 5mph:(-25-110
stuff i haven't done yet so its in no particular order some one who has can compare the advantages.
bigger carb- you will have to open up your reed block to take advantage of this. a fz 50 carb bolts up (14mm) a deltoro flange mount kinda bolts up, you can make it work your bolts will be at an angle though. 10-150$ ,probably closer to 100.
kit- elusive there are 2 in the usa nate bandits and some one else <quaterkick.com> will get more next winter? maybe any way it isn't soon. you could buy one for a Morini scooter engine but it probably won't bolt up and no one has done it before, that i have heard of.
over boring-can be done will add 3 cc and do nothing for top speed. useless unless if you messed up your cylinder and piston and have a friend who can do it for free. i know i used to say it couldn't be done. this idiot check his head yup its aluminum and assumed so was the cylinder , its not.