I have a 2014 Mercury 9.9 Pro Kicker and had problems with the carburetor. Had to have it serviced twice because the jets got gummed up from using gas with ethanol even though I used Stabil and Quick Clean 2. Mechanic said the jets are so small so they could meet EPA regulations or something like that. If I recall Mercury doesnít warranty the fuel system because of all the crappy gas people can put in them. So I started using Marine Gas with no ethanol and Quick Clean 1 (which is much cheaper than Quick Clean 2) and havenít had a problem in 4 years with the Carburetor.
Another issue which isnít as costly is the engine likes to make oil. Apparently when trolling for long periods of time the gas somehow gets into the oil and it gets overfilled. I can always tell when I need to check the oil and usually end up changing it when the motor starts to act a little odd when trolling, i.e., idles higher than it normally does. Not a big deal, just change it in the middle of the season.
I always run the kicker hard after trolling and then disconnect the fuel line and run the motor out of gas.
Really wish Mercury had an EFI 9.9 Pro Kicker when I bought mine back in 2014. Even asked my mechanic if mine could be converted like they can with IOís and Inboard engines. He kind of laughed and said no they redesigned parts of the motor and they donít have any way to convert it. If they did I bet it would be very popular.