1996 mercury 4 cyl 4 stroke 50 hp midrange

[aarongd]

i have a 1996 mercury 50 hp 4 cylinder 4 stroke with carbs SN# 0G333261. i assume this is called a bigfoot? doesn't like to run in midrange. starts fine, idles for awhile then dies. floods up, then when it starts after awhile, sounds like it runs on 2 cylinders. then onto 3 then onto 4. at full throttle it runs fine, then when i bring back the throttle it starts bogging down and starts missing again. on the trailer with ear muffs, it also sounds like its missing and midrange as well. pulled the carbs and cleaned and replaced spark plugs. timing is approx 3-4 degrees TDC. also i found a airleak at #4 carb as when i spray starting fluid it wants to die, then it goes back to narmal. any ideas? ignition?? fuel??

[boats.net]

Need to repair the air leaks, and probably need to have carbs sync.