One of the easiest ways to increase your speed is LOSE WEIGHT. But for the kind of speed you are probably looking you'd have to become anorexic and probably then some. ( Hey I could pass that line up).
Seriouysly, I've got a 76 PUCK Maxi w/a 70cc kit and a biturbo exhaust. Yes, it is illegal in VA,on a Moped (less than 50 cc and not more than 35mph). I did it to mine to just to pull me up the steep hills surrounding my town so that I can get to the commuter train station. Yes, the instalation of the kit is difficult(a lot of hey watch this!, and some compound curse word sentences because the fit is "not exactly". You might want to try just the biturbo first as suggested by Rep..
A couple of cops have looked at my set up and didn't notice anything strange, however a when motorcycle traffic cop looked at it, he knew exactly that the engine had been modified. He just grinned and asked me how fast would it go. I told him I didn't know and asked him to call me the next time he set up radar near my town and we would both find out. To date, he hasn't called. You know, I think it'd be worth the price of a speeding ticket to find out. For sure, I'd frame the speeding ticket. Also, can you imagine the look on the Judge's face when he reads,"Mr. K you"re change w/speeding 49 mph in a 25 miles zone on.... on a Moped??.. how do you plead? Uha, Officer is this correct was the plaintiff speeding on a Moped??" But then again, what's not funny is all of the money for fines I might have to fork over. (Illegal motorcycle, no registration, no tags, no insurance, no mc license option on my DMV license, and speeding plus 3 pts. against my DVM license).
Good luck w/increasing your speed.