Is the shaking normal? I'm in the process of building the same engine and setup. GoKart, what stall clutch are you using? What is your top speed with the 48t and why didn't you go with the 56t?
The top speed with the 4 stroke has been 36 mph.
Then I switched to a 28 tooth on the jack-shaft to get the ratio closer to what AGK shows on their site.
The clutch is Max Torque Clutch engages at 2700 rpm