Mine will do it once in a while, but if I put a jack stand under it, so that the rear wheels are off the ground, it's running, in gear with the clutch pulled in, the rear wheels will spin, although slowly. Did you soak your clutch plates in oil, before installing them? You will also have to break in the clutch, before it performs 100%, like it should. It's kinda like putting new brake pads on, everything needs to "wear in", to work right.