50cc gy6 qmb

[Critter from the Rock]

It's stock everything, I have this picture here so maybe someone can tell me what the best route for me to go to fix this burnt looking Piston? I do need a muffler so can you let me know what is the best for it. I also thought about putting a performance cam in it while I was there. Please if someone can inform me on which way to go to gain more performance I would like to do so now while I have it down this time, like what size gear could I go for better speed in the main gears and I got a performance clutch but not the big spring didn't know what size to get there? And where is the best place to buy a variator and rollers from and what size should I get? it's a short case. And if you know the best carb to put on it. I just don't know where to buy the best parts at? Anyway I thought after I drilled a couple of holes in the muffler and it ran like new I was all good but after a few days it did it again and I found it was now before the muffler.

[90GTVert]

If you aren't having performance issues (aside from you want more... we all do), then I wouldn't worry about fixing that piston. From the pics, it looks like carbon on the internals and that's normal. You can clean them up before it goes back together. Since you want more performance, you could consider a big bore kit too.

Most aftermarket exhausts perform about the same. Look up some sound clips on YouTube and see if there's something you like the sound of or the look of more than others. Even the cheap exhausts can be OK, but sometimes their brackets don't give enough support so you may need to add your own to prevent future issues.
49ccscoot.proboards.com/thread/5841/ebay-cheap-exhaust-bracket-improvement

Re: gears... I wouldn't gear up a 49cc. Maybe think about that if you get a BBK and it seems necessary once you see what it does then. I'd probably save the cam for the BBK too, but you may get a little extra power from the cam. As far as the size of the spring, just look up 139QMB or GY6 50 springs. If you meant the stiffness, I usually go with 1000RPM and tune the CVT with roller/slider weight. Sliders are one recommendation I'd give you if you aren't using them. I don't even bother with rollers anymore. Sliders have treated me well. You may get a little better performance, but even better to me is that they tend to outlast rollers by quite a bit.