1997 225 EFI wont run or idle

I have a 1997 grady 272 with twin yam 225 efi engines with 650 hours. I have been battling issues all season after finding/removing water in the fuel tank. The starboard engine is giving me my latest headache. It starts, idles to 700 rpm then drops to 300 and stalls. It will restart after a while 1 hour but does the same thing. So far prior to this issue I changed the engine mounted fuel filter, l/p fuel pumps, cleaned the vst filter and thermostats. The last test run was awesome both engines ran/idled perfectly and with proper fuel consumption. When I slowed down to enter the marina that is when this problem started with the Stbd engine.

Please help if possible,
Bob H

With a 272 Grady you should probably have one (or twin) Racor type external fuel/water filter/seperators. Did you spin them off and empty them into a glass jar to check if they have water in them or could be filled with water? If you don't have them, buy them and install them... I'd install one in-line for each engine. If you can install them externally (outside a closed compartment) you can use a Racor filter with a clear plastic bottom and drain plug you can visibly check for water and drain off if you see it. If you need to install them in a closed compartment, you can't/shouldn't use the type with a plastic viewing cup and drain but one that is all metal (looks like a big oil filter for a car) and can only be checked by pouring what is inside into a glass jar and seeing if it trapped water. No plastic viewing cups that could crack and spill fuel into a closed compartment allowed.