After owning these little Chinese clones, I find them are superior in every way to my original Honda CT70 I had when I was a kid. First, they have much more power and an extra gear to put it to use. The throttle also operates more smoothly and precisely. They have better suspension and better brakes. They also have a superior 12v electrical system with no-maintenance electronic ignition and electric start. No more kick starting, except in a dead battery emergency. They also came with a centerstand, passenger pegs and a small rear rack, all of which were missing on my original. The more I ride them the more I like them. Definitely the bargain of the century. Considering the features and build quality, I think they are easily worth twice what I paid. I got lucky.
I recently installed a 17T countershaft sprocket (up 2 teeth) and took my little bike out for a top speed test run, now that it's broken in and running better. It has exceeded my expectations, easily breaking 65 mph (105 kph) sitting upright (and I'm no lightweight at around 220lbs.) This is way too fast for safety on these little bikes, but the gearing change should improve my already great gas mileage as well as reduce the rpm (lower noise and vibration) at a more reasonable 45-50 mph cruising speed. I was worried that it might be overgeared, but the little engine has plenty of low rpm torque and will sometimes pop an unintended wheelie if rapidly accelerating from stoplight. They are holding up well, with no repairs needed or wear observed so far. For the money spent (less than $18/ea w/shipping) and ease of installation (I just slid the rear axle forward a tad and it bolted right up) it's probably the best performance improvement for the dollar I could have made. Next up on the mod list will be a couple of detachable wire baskets for carrying a few groceries, spare gas, etc.
Here's a couple pictures of some sweet billet aluminum bar end mirrors I installed:
And a shot of the difference in the stock carb and the 3mm bigger one that gives it a little extra umph (near 10 hp, estimated from my top speed):