I have a 16HP Briggs engine on a Roper Lawn Tractor, It will run OK when just traveling, but if I engage the deck, it dies. What is the best next coarse of action.

Hmmm, sounds as though the governor may not be operating properly, could be governor spring off. Could be a seat safety bad. Yes the seat safety being bad will allow the unit to start and run, and die when the blades are engaged. Give me more info.

Ok, we are getting some where now. I can manually actuate the flapper on the carb and keep it alive, so it may be in the governor. I don't know if I have a spring, will have to look at tonight. What about the seat safety, how do I check that? I very much appreciate your help.

Jim

The "tang" or lever, that touches the seat safety may be bent a little and not making good contact with the lever. As you engage the unit and are going across the ground the bumping can cause the switch to loose contact momentarily.
I think we are on to something with the governor though. Look close to the carb, and you will see some springs, be sure they are hooked up.
If you are setting still, and running the engine at top rpms, and engage the blades, do you hear a momentary difference in the sound of the engine, it should momentarily pick up rpm, then go back to the beginning rpm. This is so hard to tell someone how to test in words.