that was my first moped, too. when it comes to performance, what you can expect without much work depends on which bike you have. assuming this is post 1978, the "C" is the fast (30mph) model. the VIN plate at the front of the frame should indicate which you have. the difference is in the carb, the intake, the porting, the head, and the rear sprocket (the 30mph one had 35 teeth, the 20 and 25mph ones had 39 teeth).
i put a Dellorto 15mm SHA carb. on mine and ported it to the spec's published in the wiki. i also had a squish band milled into the head. when i was done it ran 31-33 pretty consistently. what you're after is attainable. i've also read that putting an old style motobecane "blunderbuss" exhaust on there will add speed (mostly top-end), as it's less restricted than the newer ones (like the one on the model 7). lightening up your clutch would help with acceleration, too. if you have a slower model, you'll want to replace the intake and rear sprocket. replacing the intake would be tricky, as it's actually part of the motor mount. your best bet is to find a model 7 intake from a 30mph model. you could also reset the timing so it's 1.7-1.8mm before TDC. of course you can also kit it, but try these things first.