Pony pukes out a large clouds of blue smoke
HI, I have a Troy-bilt Pony with B&S 17.5 horse. Run great for the last mowing, although was backfiring somewhat toward end of day, but still ran good otherwise with plenty power. That was a couple weeks ago(it's been sitting since). Yesterday I went to mow and it started fine but when I engaged the deck drive it sputtered and puked out a large cloud of blue smoke and lost power. Tried a couple times and gave up. It idles fine but on high throttle it will run fine(some sputtering) for about a minute at a time and then puke the cloud of blue smoke.
Longer story(background). I acquired this mower last fall as it was included in my home purchase. I used it a couple times and all was good. Before the last cut(first cut of the season) I changed the oil. Not knowing what oil had been used, I put in a synthetic blend Valvoline MaxLife 10-40 as this is over 10 years old. Was that a mistake or just coincidence?
I have a mechanical background(now retired) so am capable of carrying out any necessary repairs. Just need some direction. Any views would be helpful. The grass is growing fast!