I infer that the Mercury 90 FOURSTROKE carburetor engine is probably also a c.2005 vintage and came with the boat as the original engine.
There is a good probability that this engine is actually a Yamaha power head engine. Around c.2005 Brunswick had not developed its own four-stroke-power-cycle engines, and Brunswick entered into an agreement with Yamaha to buy engines from Yamaha. Brunswick then repainted and rebadged these engine under their Mercury brand. Most of these engines used carburetors. Only a few Mercury-badged Yamaha engines were produced with electronic fuel induction (EFI).
Considering the overall general trend for use of boats to be at sea level or not much higher than perhaps 600-feet above sea level and to be in temperatures ranging between 60 to 90-degrees, there was and remains really nothing wrong with carburetors in those conditions, and carburetors were used for decades.
There were reports of problems with the carburetors on these Mercury-made-by-Yamaha engines. The problems seemed to be associated with the very low rate of fuel flow at low engine speeds (like at idle). The carburetors were reported to become clogged. I believe that these were real problems for some users. You can find many prior discussions about these problems in the archives. For example, here are several old discussions on these engines:
Mercury 90-HP FOURSTROKE: Carburetor Problemshttp://continuouswave.com/ubb/Forum3/HTML/009936.htmlMercury 90-HP FOURSTROKE Carburetor Repair Billhttp://continuouswave.com/ubb/Forum1/HTML/015765.htmlMercury 90-HP Four-stroke Unreliable; Carburetor Problemshttp://continuouswave.com/ubb/Forum3/HTML/009067.html2004 170 Montauk 4 stroke carburetor problemshttp://continuouswave.com/ubb/Forum8/HTML/002726.htmlIf you read these threads you will find first-hand accounts from people who owned the engine. You will also find comments from people who did not own the engine but were enormous fans of Mercury-brand engines who attempt to lay all the blame onto Yamaha. You will find comments from very experienced mechanics who owned these engines. You will find comments from people who were not mechanics, who did not own the engine, and who were big fans of Mercury. You should consider which sort of comments will have the most information value.
As for the care and feeding of these c.2005 Mercury 90 FOURSTROKE engines, I suggest the following:
--do not intentionally try to drain all the fuel from the carburetors between uses
--stow the engine in a vertical not horizontal or tilted-up position to minimize fuel draining out of the carburetors
--always treat the gasoline fuel with a cleaner additive; Mercury makes several such fuel treatment products, as does Yamaha, as does Evinrude, and as does many aftermarket providers
--try to use high-detergent gasoline from major fuel providers, and use ethanol-free fuel if available in preference to blended fuel
--use a 10-micron fuel-water separating filter upstream of the engine to ensure that no water or particulate debris gets to the carburetors
--avoid letting the engine sit unused in warm temperature and strong sunlight outdoors for weeks between uses as those conditions accelerate fuel evaporation
--before engine start be sure to prime the fuel system with the primer bulb until the primer bulb becomes firm
--before engine start carefully read and follow the engine's exact starting procedure; every engine has its own starting procedure with its own peculiarities, and do not assume you already know how to start engine and use some different procedure.