Scooter Rebels is an excellent site for info...
http://scooterrebels.proboards.com/
There are larger and more prolific sites out there, but Scooter rebels is kinda like this place, smaller, more of a family type aire to it, and jam packed full of info. Severral of the larger sites were started by former Rebels, that were more into drama that scoots, they couldn't deal with the laid back atmosphere...
But enough about SR, yuh, those 50cc scoots work really well, and will bump up to 70cc easily. fact is, I think I still have a complete 70cc kit, in the box out in the shop. I'll cut you a deal on it, if it's still there, and you want it.
Be sure to change out the fuel line too. Unless the Chinese have improved the fuel and vacuum tubing, it sorta self destructs from the inside out, really making a mess of the carb jets.
And like has been said, check everything for tightness, and replace the plastic fuse holder for an aftermarket holder that uses a blade type fuse. Those cheap Chinese glass fuses do not impress me...LOL.
PS, I port heads on the 50cc QMB's too.
DOUBLE PS.... YUP, I still have 1 kit, 72cc bolt on piston(w new pin & clips) & cylinder, Big valve cylinder head, rings, gaskets, SS Intake and exhaust studs, and a perf cam, $100.00 shipped, or $130.00 if you want a mild porting job on the head. Mostly just a clean-up of the metal flashings, and some bowl work under the valve seats. Don't need to do much polishing on these smaller heads, as they work better with a slightly textured intake, and a semi polished exhaust. The textured intake, keeps the gas in suspension, and the slight turbulance keeps it vaporized, too smooth in these small ports and the gas will condense into droplets and not perform well at all..
Lemme know if you're interested. I only have the 1 kit.