Maybe the choke is sticking.

Blue smoke is oil burning. Maybe you overfilled it and some oil seeped past the rings. Check the oil level. You also might have a compression test done and see how the rings are.

there is no choke on this model....at least none I adjust. I acvtually could add a little oil....which I could have sworn was full a month ago. If its the rings, what does this cost to repair...I assume its a dealer repair...not something I could do...

Generally speaking, it is not cost-effective to do major engine repair or replacement on most mowers.
Your engine is most likely running rich, which causes carbon build-up. It also burns oil because the excessive fuel in the cylinder picks up oil that gets by the rings and burns it. This in turn causes excessive carbon to form in the piston rings, 'freezing' them and preventing normal expansion.
In this engine I would make sure the oil used is SAE 30 HD, and I would have the shop fix the fuel delivery system. Then I would continue to use it while using Seafoam in the oil and gas. This most likely will take care of the problems it now has. If you do this, check the oil frequently and change it when it gets dark from cleaning up the engine.
You also need to immediately verify that the air filter is not clogged with debris.
Another angle that can explain the carbon is the use of old, stale fuel. Always use fuel stabilizer in your gas can.

Sax is right on the money. After you give it it's check and oil change, install an inline fuel valve. Good insurance.

re:Generally speaking, it is not cost-effective to do major engine repair or replacement on most mowers.
Your engine is most likely running rich, which causes carbon build-up. It also burns oil because the excessive fuel in the cylinder picks up oil that gets by the rings and burns it. This in turn causes excessive carbon to form in the piston rings, 'freezing' them and preventing normal expansion.
In this engine I would make sure the oil used is SAE 30 HD,

*Yes thats what the dealer sold me.

and I would have the shop fix the fuel delivery system.

*Can you elaborate....what is broke?

Then I would continue to use it while using Seafoam in the oil and gas.

*I usually run seafoam the first few tanks each spring then move to Stabil though the gas seldom sits more than a few weeks. I started using an ethanol additive this year too.

This most likely will take care of the problems it now has. If you do this, check the oil frequently and change it when it gets dark from cleaning up the engine.
You also need to immediately verify that the air filter is not clogged with debris.

*It very clean.

Another angle that can explain the carbon is the use of old, stale fuel. Always use fuel stabilizer in your gas can.

*no, not old, see above.

So is the engine pretty much past its prime. Should I have expected it to last longer than 12 years?

Considering your other post, and if you are leaning towards a new one- is this mower worth repowering? If you were to search with the model and type # of your engine- you may find a deal on new repacement engine for ~ $150 or so. Toro's use a larger crank bolt so the spec needs to be the proper replacement. Or post the #s here.

yea but how much life is left in the tranny....

12 years is great for a mower - I would have no qualms about replacing it. Based on the new info it would seem that the engine (rings, cylinder, piston) is worn out, but a penny-pincher could get the carb overhauled and probably use it several more years.

...maybe keep it as a back up and have a bunch of spare plugs lined up..

You won't need the plugs if the carb is fixed - they can smoke a little without fouling the plug.

just clean up the fouled plug with a brass brush and swap it back in when the present one fouls . Rinse and repeat. A high float level or a chunk of dirt in the needle valve could be causing the over richness. This in turn would raise the level of the oil to wash past the rings and burn. Check the oil for a gas smell and change it if it is gassy. I wouldnt be junking this mower just yet.

can I get at the carb myself or is it difficult...I have serviced my crab on my snowblower...but I can see it there...

Not familiar with your particular mower, but the carb is under the air filter.

12 Yrs is not all that Bad if the Engine Oil has been changed regularly along with proper air filter maintenance. As suggested I would start with the compression test to verify the stae of condition of this engine . Old plugs (black) not oily are not an issue just normal ageing . Dark brown is ideal over a few yrs of service.
Since your agenda is to have a back up second unit that will not be seeing a lot of usage I would just add some fuel conditioner to clean up any residual carbon within the cylinder head and rings and valves which could be as advised the primary reason for your plug and blowby issues . Good luck you have a very capable unit model .

I'm having the same problem. I thought it was the carb but that's not the case (carb was cleaned and a repair kit installed) and I've been using fresh gas with Sta-Bil all season.

My next step is the ignition system. I'm wondering if the spark plug wire has become loose where it connects into the boot. I'm going to start there and work my way up to the coil/magneto to check for rust/blockage.

The mower starts great and stays running, I just hear a random popping sound from the muffler while its running and don't see any smoke and no fluids near the muffler.

Changed the spark plug at the beginning of the season and just a week and a half ago and the air filter was changed about a month ago and is clean.

Andre: Another point of consideration if your Son in Law did indeed identify a wet (Gas Soaked) plug is that the gum or debris within the carb has not allowed the fuel inlet needle valve to close completely , which can cause an overrich condition. Usually unless you have a manual fuel shut off this wil cause a potential for flooding the oil within the crankcase fuel. In any case check you oil level and verify by smell if oil is gas contaminated .

Woody : You scenerio sounds more likely coil or perhaps air gap issues perhaps due to corrosion. The popping could be a sign of a weak coil indeed. I would 1st rule out a bad plug wire or boot as you have indicated. Then confirm the other previous coil potential issues . Usually coils will so problems intially when engine has met warm up temperatures.