Any tuning on your part would either cause a power loss or simply shift the power band from a useable inclining plateau to a peaky curve aroiund the top end (as seen on a dyno chart). The best thing to make your 70cc go fast would be to buy a service manual and ensure the maintenance is up to par. Make sure your ignition timing is right on the mark, replace coils if spark is weak, keep your air filter in pristine condition, and be sure your tyres are properly inflated. Do not "gear up" your sprokets unless your bike is properly tuned and revving at redline in top gear. Otherwise, you simply increase the bearing load and get closer to an overheated or friction-welded/seized piston You can also go over the bike and remove any accessories that are not needed to lighten the load on the bike. The bike isn't only carrying it's own weight. You, the rider, are a significant factor - the only weight that doesn't contribute to the bike's power output. Be certain that you aren't carrying any weight that doesn't contribute to your own power output. Then again there's the old addage, "There's no replacement for displacement." You may have overgrown your little scooter. I personally believe one is safer on a motorcycle anyway as teenie wheels and imbalanced front/rear weight bias scare me. Happy riding. Edit: <quote>david askari: power and speed not always go together</quote> David, what the $@#! are you talking about? This has nothing to with the answer submitted and for the record is incorrect. Power output is directly related to resultant speed.

A 70cc four stroke is probably a honda. Since you are interested in increasing power, not speed, I will guess you have a trail bike (Honda XL 70) with a 4spd transmission. The other popular model is Honda passport (us name) with the same engine and a 3 spd semi automatic transmission. The trail bike can be modified for less than ten bucks if that all you do and rarely use you 4th gear or go past 30mph. Mostly you climb hills and go through dirt and rough terrain. Change the drive sprocket (the little one by your foot with the chain on it) to one less tooth. A sproket from a honda z50 will fit fine. Now you can go up that hill that you almost could make in first gear but stopped short a few feet. There are other things like keeping it tuned as mentioned by the first answer. Power=uphill incline in this answer and speed=mph. Bad english does not always mean a answer is wrong.

Sell it before you mess it up, and cant sell it for scrap. buy a small motorcycle and save yourself time, and headaches.