In my experience, 99% of time I've seen this, it's almost always the oil to gas ratio is mixed to high. I'm also always told everytime, the mix is 50:1, so it has to be mechanical.
Mistakes happen, someone grabs a 2 gal mix for 1 gal or a 2.5 gal mix for a 2 gal gas. Even at the dealer, the help could have screwed up the mix that was put into the unit.
Almost always, I replace with new fuel mix and run it for a bit to flush the excess oil out first, then pull the muffler off and wipe out the exhaust port, rinse out the muffler and spark-arr ester before it bakes on. 99% of the time it goes away with just these steps. It's also always best to replace the fuel before breaking down a carb, if not, to find out later that its was in fact the oil mix was in fact to high.
Your dealer will take care of you, but it would also be a good learning experience for you learn how to take care of your equipment at a young age, by attempting a simple problem solving first yourself.