In my case it was blue smoke and the engine was a 2-cycle, a Dolmar
chainsaw. I bouhgt the saw second -hand for a brushing project, where
we had to cut alder trees about 2-5" in diam. A couple of days into the
project, bush camp, I woke up sick, went out, filled my jugs from a 5
gallon jug we kept under a tarp there, and rode up to the job site. Of
course the fiver was full of kerosene for the space heater, and i was
so plugged up i never even smelled it. The saw was full of gas from the
day before. I ran three tanks of kerosene through it before coffee,
blowing smoke like a house on fire, and finally got over to where my
buddies were, asked to borrow a tuning screwdriver, get the piece of
%$* to rev up right. "Did you spill kerosene on your pants this
morning?" somebody sez, handing me a screwdriver and sniffing the air.
Yeah we had a good laugh about that.
No harm done, and that saw ran till it shook itself apart many years
later.

JohnK