my back wheel is jammed?

Take the chain off by springing the split link apart (if it has one) or by slackening the spindle nut and moving the wheel forward- at least you'll then know if its the wheel or something else thats at fault. You won't be able to tell if there's an engine problem at this stage as there is a centrifugal clutch between the engine and the chain drive sprocket.

John
March 2008