How do you tune a 1982 Kawasaki KZ750 twin's cam chain?

The bike wants to start, but gas is leaking back into the air intake and igniting, causing smoke to come out from under the seat. I'm pretty sure this means that the engine is backfiring or the valves are staying open when they should be closed.

It could also mean that your spark is too far advanced and igniting the fuel mixture while the intake valve is still open. Check your timing and also your auto advance mechanism which may be stuck.