Ok so a while back, I finally got my schwinn skyliner with Hua Sheng / Grubee gearbox with a 48T rear sprocket going. Soon after, the key that holds the output sprocket from the gearbox on the shaft sheared in half. I have fixed that problem and changed from using lithium wheel bearing grease inside the gearbox to using half synthetic gearlube and half motorhoney engine stopleak. Sometimes, I can get up to about 32 mph. Sometimes the top speed is 21mph. Sometimes it oscillates between the 2 speeds in one trip. I am having difficulty figuring out exactly what the problem is. With the way it's geared, the top speed should be MUCH higher. There are those on this forum that claim to be able to get up to 40 mph with a similar setup. Top speed aside, the fact that my speed is so inconsistent really bothers me. IS this a problem with the gearbox? Is the clutch just not engaging properly all the time? Or is this an engine problem? I have about 100 miles on this engine; is it possible that it just needs more breaking in? Please help.