need help fixing my bike and ideas? wheel wont spin under load?

[kieranemillswatts]

i have a continuously variable transmission(C.V.T) on my bike. if you know anything about these it would be helpful. when i lift the back wheel off the ground it will rotate if i rev the engine. but if i put the wheel on the floor and rev it nothing happens.... any ideas?
yes it is a belt driven one.the belt may be slipping, how can i tell?

 

[Robot1]

Is the belt spinning? It could be too loose.