1974 SS16 Onan engine quit while mowing

Been a while but I'm back. I almost swapped this old Onan out a couple of years ago but did not , I almost wish I did. I was mowing the lawn yesterday and all the sudden she shut down just like I turned the key off. When I tried to restart the engine it just drags like the battery is low but it has a full charge. I replaced the ground cable with a new one and tried again today and have the same problem
The engine was a little beat up , broke down and worn out ( a lot like me ) before this problem but I have always been able to get it going again. Not this time though . No knocking while it was running but smokes a lot .
Anyone have any ideas ??

I pulled the plugs this morning and she will turn over but makes a heavy whining noise as it turns. I have replaced the starter twice on the mower in the last five years. The last was last year.

OK. Problem solved for now anyway. Pulled the deck inspected the bearings in the spindles , greased everything , put everything back together . Turned the key and the engine started and ran pretty good with no further Problems. Finished mowing the lawn that took about 45 minutes and everything seems to be good to go now . I Dunno.
thanks anyway--------A.B.

HI BRUCE
BEEN WANTING TO REPLY TO YOUR POST AND THOUGHT BEST NOT TO DO SO, OH WELL MY THOUGHT WAS THERE A PET ON THE END OF THE CABLE OR CHAIN YOU WRAPPED AROUND THE BLADES,WERE YOU TOO EXCITED TO REMEMBER TO RELEASE THE LOCKED UP DECK MULE DRIVE, SO TELL US WHAT GREASING THE SPINDLES HAVE TO DO WITH ENGINE STARTING. ALL MAY LEARN SOMETHING.
HANG IN THERE
JIMMY

Ok Jimmy , guess I'll fess up a little. I did realize that I still had the deck engaged when I was trying to start the engine and it was draggin the engine down enough that it made it difficult to start. That is not to say that I have not started it with the deck engaged many times.
 However, the mystery still remains as to why it just quit in the first place . It just shut down as if I turned the key off. It did the same a couple of weeks ago as well. I should mention that it has begun to backfire through the exhaust as well now and then and has a tendency to shoot sparks out the exaust as well when it has been run long enough to mow my little acre here.
 I have no idea of why it will now start and run pretty good and I continue to use it at least weekly to mow and to occasionally tote my bug killing spray setup and weed spray set ups with no further problems.
  I can say with certainty that I dunno. 🤔
   A.B.