Something strange is happening !

Hello , I have a John Deere 170 (1989) that still is a fantastic machine to this day ! A few years back , the safety switch connection for stopping the blades when you get off the seat broke , but I didnt care as I get on and off frequently and I am aware of the blades turning and am careful . So there was never any problems . I purchased and installed a new battery for it in May this year . I was very ill for 4 months and didnt use the tractor at all . When I finally did use it again , the engine would stall when I turned the blades on via the pto switch . Having needing to sharpen the blades anyhow and after removing the deck (checked that out as well and deck pulleys were good and free spinning) , I tried again to engage the blades and it stalled again . Thinking the pto clutch maybe was binding , or rusted due to a few "wet" grass cuttings , I removed that and sat it on the ground and tried again and it stalled again ! Thinking it was the pto switch , I went and got a new , installed it , and the engine still stalls ! I am stumped as everything was great 4 months ago , it sat in my shed , I go to use it , and now this happens ! Any thoughts on this ?