50 hp 4 stroke with cough

I have a 2000 50 hp 4 that is driving me nuts. have had intermittent trouble with coughing, hiccupping at *****ing speed, stalls ocassionally when I give it throttle. Have had all carbs adjusted with mercury tube deal, checkd compression, replaced thermostat, fresh gas, new plugs, new bulb and gas lines (removed gas line connector - now straight shot to filter/carb...). It sat for a couple of months over winter - took it out two weekends ago (trailered it for about 30 miles) - ran best ever...not a single issue. took it out yesterday - coughed, hacked, stalled, hard starting...rough idle one minute - next smooth as silk. (Weather was identical both days). Water seperator is clean. In the yard with FW flush attached - cranks up easily when cold - warmer it gets, rougher it runs...then sometimes smooths right out and purrs, the - no reason - back to rough - seems to be okay at high end .....help

oooo-kay...hmmm...I have been rebuilding carbs for years on small O/B's, motorcycles, lawn mowers - is this something I can tackle? That set-up looks pretty initmidating - friend who's a recently retired yam mechanic says it's not something I should try.... will I have to re-sync them again....?

[boats.net]

Without carb sync tool it would be difficuilt to get running right.

my mechanic buddy has the sync tool - he set it up and checked it for me once before - I just hate to ask him to pull and clean the carbs if I can do it. He's facing rotator cuff surgery next few days. Is there any kind of spray treatment / fuel additive that MIGHT help that you guys recommend?

.........mommy...........

thanx!