Uhh, .... that’s not good.

[Mr Lee]

I never finished picking up all the leaves in December so I tackled that today.  Then fired up the lawnmower to chop up the stragglers.  When i had a few passes left my mower, which is a 48" commercial walk-behind, started sputtering and dying, then spewed out very thick white smoke.  I mean THICK dense smoke!  So i shut 'er down quick, pulled the dipstick and it was covered in almost pure gas. 
I'm guessing this mean something happened to the rings?  And if so, hopefully thats it?  It only ran a few seconds while it was smoking so I'm hoping the rest of the internals are ok.






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[Chryco Psycho]

Depending on if it has a carb or FI the repair may vary but the fuel system probably flooded the engine forcing fuel past the rings

[jimynick]

Is this a air or water cooled engine? If water cooled, usually white smoke indicates coolant in the combustion chamber and that's usually due to a head gasket failure. 

[73chalngr]

For some reason fuel is getting into crankcase when not in use . Change the oil and install a fuel shut off valve . Close the valve when not in use .

[Brads70]

 

The needle and seat has leaked and filled up the crankcase.( dirt, debris ) When it is over full usually there is a vent and it gets forced up the vent as it has no where else to go. Usually this vent is near the carb so a smoke show usually ensues . You might have damaged the engine but at this point all you can do is change the oil and see what happens. Like mentioned above , add in a fuel shut off valve to prevent it from happening again.

I see this quite a bit, usually with Biggs engines. Most of the time after an oil change( and filter if equipped )  your good to go but there is a chance the rings, bore, piston got damaged.  Have a look at the air filter to make sure its not soaked with oil/fuel

[RzeroB]

I had a similar thing happen with my mower, an Exmark 54" with a 26hp horizontal v-twin Briggs engine and about 500hrs on it. I did a careful tear-down and found that one of the cast pistons had failed with a tiny hole right in the center of it. The hole almost looked like it was punched out ... but there was no other damage to it or the engine. I figured it must have been due to some kind of metal fatigue??. Rebuilt the engine and it's still running fine to this day.

[Mr Lee]

All good advice.  Thanks guys. 
It's an air cooled Kohler engine.   I think the needle and seat sounds like it could be a likely culprit. Will start there and hope that it wasn't running with gas in the crankcase for very long before I shut it down.


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