Well after two visits to the dealer my issue still exist. They could not duplicate the issue, they checked everything and found no problems after keeping it for almost 3 weeks, he even checked in his system for other mowers sharing this issue and found none. The shop mgr said they put enough time into it... I may be wrong but after some thought I think it's the design of the exhaust heat shield below the carburetor bowl combined with the lower boiling point of ethanol blended fuels, when the engine shuts off it generates more heat causing the fuel in the bowl to boil creating fuel vapor. The muffler and heat shield is very close under the bowl. At 30 hours on the clock it still continues. It starts fine cold, it runs great mowing and instant hot restarts are perfect, say a minute or so to grab a soda but if it sets for 5 minutes it will puff black smoke for a split second, run a bit rough and clear up. If it sets 30 minutes no black smoke so it's gotta be heat related, the boiled over fuel vapors evaporates but that's my take on what's happening. This winter I used the mower and it was flawless on hot restarts but now that temps are in the 80s it's starting again, the hotter it is the more prone it is to occur. I may try non-ethanol fuel and see if this resolves this ongoing issue just to see if it helps. My mower has the newly designed hood, I recall the dealer mentioning it was the first he had seen when they uncrated it, perhaps the old design allowed more airflow, suppose I could try running it with the hood off and see if it makes a difference. Is it normal for these Kawasaki engines to "occasionally" puff blue oil smoke at cold start, I've had it happen 3 times? I've changed the oil twice by the book at 8 hours & 1 year interval and the oil level is dead on & not overfull. I read somewhere the way the cylinders lay this can happen depending on where the piston stops? I asked the dealer about this as well and he said it is still in the break in period and can happen. I agree with Mad Mackie, eventually this extra fuel/vapor will eventually cause wear on the cylinders but not much I can do when the dealer cannot find anything wrong which is my issue.