I seen this mower advertised online, Murray riding mower. 11 HP , 30" cut , 4sp &1 r ,Runs good, Stalls when ingaging mower deck belt. May be adjusment? $130.00 takes it
Any ideas what might be causing this and would this be a good deal for this mower.
Thank you for any help you can give me..

Looks like a good deal to me. It might just be the "reverse" switch.

If it thinks reverse is enguaged and you try to enguage the blades it will die out. It's a common problem on newer mowers with that safety feature. Also the motor alone is worth that much.

Sounds like a 20 year old mower ,
I wouldn't pay that for it.
But that's My opinion .
I buy and sell mowers all the time .
I have 2 or 3 that sound just like that one in my junk pile.
Luck

Dis-connect the kill wire coming out from the shroud. Its usually by the starter . Then start the mower and see if it stalls or not. If so go through the blade sensor and the neutral sensor to see which one is bias . Good luck. Post results if you can