Look carefully at the brake lever setup on your machine. You should have two cables coming out of the perch. The top one is your actual brake cable. The bottom one is the reverse cable. Look under the brake handle and you'll see an extra moving piece there with the reverse cable attached to it. When you push the red button on top of the handle (BEFORE pulling the brake lever) all you are doing is popping out a little peg that catches this reverse lever. So when you pull the brake handle now, the reverse cable gets pulled.
Just follow this cable down the machine and trace where it goes. You should be able to follow it to the engine and see if it moves.
- Frank
1984 200ES Big Red
1985 350X (x2)
1986 350X
1986 250SX
1984 Auto-X
1984 ATC70
1985 ATC70