2003 75 HP 4 stroke 4 cylinder carbureted outboard will not idle

[jdlloyd_iboat]

I have a 2003 Mercury 4 stroke 75 HP 4 cylinder carbureted outboard that until this year has worked without too many problems. I have not winterized as I have a lift and have been able to drop the boat and run the engine occasionally through the winter. I use STABIL for ethanol in my fuel. This spring I noticed that I could not start the motor at idle. I had to advance the throttle to get it started and then could pull it back to a proper idle at neutral after it warmed. However, I noticed particles in both my filters (an inline and one on the engine just before the pump). The inner core of my gray fuel line was coming apart. I cleaned out the engine filter reservoir and replaced the inline and the fuel line, however the engine filter caught some additional particles that had not flushed from the black line inside the cowl. I cleaned and flushed again but idle was unimproved when cold. I ran the lake this past weekend with old fuel and the longer I ran the better it seemed to work until I started adding fresh gasoline oddly enough. Then it would not idle at all and I had to swim the boat back to the dock. A few days ago I removed the carbs and took each apart for inspection. The needles were OK and the floats were good with proper float drop. The only thing that looked abnormal was a stubborn crystalline coating in the bowls. I rubbed that out with some brake line cleaner to preserve rubber parts. It washed off OK. I blew out passages without disassembling any of the jets or seats. I reassembled everything with no new parts. All rubber looked OK. I checked TPS and throttle settings and removed and inspected plugs (looked OK a little black non-oily discoloration on each) and gapped properly. The plug wires were all within resistance spec. Engine still will not start at neutral when cold and has to be advanced to about 2000 RPM (per boat tach) to start and warm the engine. When I drop it to a little above 1000 rpm it will run with some hesitation and a random coughing every 10 or 15 seconds. When I drop it back to the neutral idle position it will stumble and die. I can start it but it will not continue to run even when warm. I have added new fuel when I was cruising this past weekend so it should not be a stale fuel problem. I also kept the old small filter on the engine filter housing after backflushing it with brake cleaner. I have a new filter that I was going to use after I knew all the particles have flushed out although I am pretty sure I am there. I do not think it is this filter because it flows plenty of gas at higher RPM. Should I Sea Foam it? Sorry for long post but I have spent a few hours puzzling this out and I wanted to share it all. I used a SELOC manual to perform the work.