ya. just putting on a 13 mm carb really does nothin except change engine characteristics and give you the ability to say you put a more expensive carb on it. it wont do anything until you drill out the intake to 13mm, so the intake doesnt act like a bottle neck. better yet is the 24 mm carb kit from polini, but they arent worth it unless you are planning on adding a 90cc kit and tons of ather stuff which would make your bike unreliable and a pain to start. personally, i would drill out the intake to 13mm, bolt on a 13mm carb, and put on a nice expansion chamber exhaust on. dont worry about a kit. they suck gas. best fuel mileage and speed would come from 50cc. the expansion chamber keeps more fuel in the cylinder and not out your tailpipe, and the only fuel economy reducing item is the carb. your fuel economy will be about the same, and you can easily expect about 45 mph out of your ped, with snappy acceleration.