Ran a 90HP Merc on the flats boat for 7 years until selling last year. Prior to owning that boat, had a Yamaha, but never had a problem with that Merc motor. Couple things mentioned above are very good preventive measures. Seafoam and STA-BIL are your friends. Run ethanol free gas as much as possible. If there's one candidate that'll screw with an outboard, that ethanol is it. Stay away from it as much as possible, if you can. I also installed an inline fuel filter that mounted right on the transom. Twist the petcock, drain the bad stuff, and bingo.. back in business.
I've had a 90 hp, EFI Merc 4 stroke for 5 years now. I'm very satisfied with it. Only time I had a problem was
once using ethanol gas. It took a lot longer to get the bad gas out than it took to get new back in. DO NOT use ethanol near the water. The two don't mix.
