all things mentioned...fuel line,plugs,fresh gas,carb clean-re-build,and def sea foam,if it was sitting for that long. If you do those things and still have an issue,look towards an electrical issue.Had a classic 50 do this,and ended up being the switch box.Was sending full voltage to cylinders 1 & 3,but intermittent on 2 & 4. Ran great,started great,idled up,throttled up then bogged,farted,bucked like fuel ,but was electric. Just did the seafoam on a 25 hp my son was given at his Marina job. Motor spent years in saltwater,never flushed. cleaned her up,and runs smooth. Good luck.