New problem on G6200

[wwr1964]

Updating my progress on getting my late fathers G6200 back in service.
I now have the tractor running. I took off the mower deck and replaced the belt and freed up the belt tensioner. After reinstalling the mower deck I took it out to see if it was cutting even. The tractor now will not run while the mower is engaged. It takes it a second or two then starts to die until I disengage the mower?
Air still in the fuel lines? This only happens if the mower is engaged otherwise it will pull fine if I just ride it around the yard.
Any help is appreciated.

 

[Baby Grand]

Operator presence switch at the seat?
I think it activates when the PTO is engaged, which may explain why engaging the PTO kills the engine.

 

[wwr1964]

Well its not the seat switch. It will run for about a minute with the mower on the just starts to die.
I am completely clueless as what else it could be. Head gasket leak?

 

[Baby Grand]

With the PTO released (and engine OFF) do the blades spin fairly easily?
Wondering if it's a seized bearing in the deck or PTO driveline ...
Do you get a lot of smoke when engaging the PTO - either engine lugging smoke or belt slipping smoke?