The Raleigh Chopper and similar bicycles all suffer from a fundamental design flaw. The centre of gravity is too far back. This means that the front wheel has too little weight on it. This, combined with its small size, leads to "speed wobble". The front wheel and handlebars will start to osscillate left and right, faster and faster until the bike goes out of control completely, throwing the rider in the air. There is no way to stop this happening.

Carefully dismantled, an original Mark I or II Chopper will yield the following spare parts:
SA AW hub gear
26 tpi headset and bottom bracket
standard Raleigh chainset and pedals
brake calipers and levers
 
The Mark III has lower quality components but is still worth having for the rear hub.