Intermittently Hard To Restart (2004 Mercury 150 EFI)

[hawghunter10]

I am having an intermittent problem starting my 2004 Mercury 150 EFI. Engine starts fine @ launch but after 10-15 min run to first stop(then fishing for 15-20 minutes) it is sometimes hard to restart. This may happen several times per trip, only once a trip, or some trips none at all. When the issue arises, it will turn over but spits and sputters after releasing ignition switch. The remainder of the time it fires right up as soon as the switch is bumped. One beep self test working fine when turning ignition on. However, I am getting a one beep alarm while actually turning the engine over. This additional alarm doesn't necessarily relate to the restart problem...in other words, sometimes it alarms while turning over and starts and sometimes not. Mercury mechanic checked everything out on computer 3 times and says it all looks good. I recently installed a new fuel-water separator on the boat & engine, oil filter on engine, fuel diaphragm kit, impellor, & correct plugs. Anyone out there had a similar problem that might could lead me in a general direction to get this resolved? This is driving me crazy!