I have a 17hp B/S on a John Deer Saber. Just had new coil and alternator installed. The motor runs good, but it is surging. What is the problem and how do I fix. Also It has a safety feature where you can not mow in reverse. Would like to disable this if possible.

Have you checked the vacuum tube from the heat shield down to the carburettor?

Could be fuel related, contamination, or blockage.
As far as the reverse safety, leave it alone.

That was next, but to be honest, I've seen some vacuum advance (if that's what it is) issues relating to this black pipe before