Mariner 60 running rough/bogging down

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Hi everyone I bought a boat a couple of weeks ago with a 60hp 1990 mariner and it hadn’t been used for over a year, half the time it’ll run great with no issues whatsoever and other times it’ll sound and run rough especially when I try to up the rpm at all, it won’t go any faster,. I’ve drained and refilled all the old fuel replaced filters but didn’t change much. What are the common things I should be checking/ replacing? Thankyou