I got the carburator completely apart, cleaned, reassembled and mounted.
But another problem has developed.
The engne runs fine without using the mower, but when you engage the mower the engine bogs down dramaticlly. However, when I push the coke lever to about a third of the available movement, the engine picks up and the mower and tractor run smoothly.
I have removed and cleaned the pilot jets and they are fine. I reinstalled them to the settings as I found them, 3 1/2 turns from the bottom. I then tried 3 turns out, followed by 4 and 4 1/2 turns with little or no difference the the engines operation.