MERC 90 4 stroke won't start

Hello All,

I'm having an issue with my 2002 mercury 90 outboard 4 stroke motor. It cranks but it does NOT run for more than 10 seconds. Because of this issue, i just finished replacing the inline fuel filter, spark plugs, oil, old primer bulb (lines must not have been ethanol resistant cause they were gummed up bad), cleaned the 2 fuel pumps out (had a little amount of that plastic corn looking gunk from the line), checked all other fuel lines (which appear to be clean after the fuel pumps), drained all the gas and connected the motor to an external 5 gallon tank with seafoam. The motor sounds exactly like it did before all of this. It sounds like it wants to start but nothing happens; when it does start it runs really really rough. I did take the plug wires out and from what i can see on the diagram in the book from top to bottom they are connected as 1-4 2-3. I'm at a loss. Any ideas?!?
Thanks in advance

UPDATE for anyone reading: pulled all 4 carbs off...but before i did, i squeezed the throttle and noticed that 1,2,and 3 shot out gas...but 4 did not. took it apart and the jet was fully clogged. hopping this is the cause and the cleaning will fix it.

troubleshooting pays off again!!good luck boating!!

so to bump this back up...a few weeks ago i took all the carbs off, cleaned extensively (done by my friend who is a car mechanic). Put everything back together and it ran but only with the idle screw tightened too much and would stall under throttle. Frustrated, i brought it to a boat mechanic. After waiting two weeks for it to just be looked at i went by to check up on it today and they happened to have it out working on it. I asked what was wrong and they said the carbs were dirty...I told them that that can't be because i had just cleaned them and it sounded like a vacuum tube or something was off. They insisted that the carbs must be dirty and it was only running on 2 cylinders...I found that odd since when i took the intake off i saw gas being sent through the first 3 carbs but not the last one (which changed after i cleaned it). The boat mechanic said that the carbs have a bunch of intricate parts and they need to be taken apart (which we did).

Did i miss something? Long story short, when they said carbs i told them to stop what they were doing and i would pick it up tomorrow. They also quoted the carbs at being $1000 worth of work just to clean.

Any thoughts from more experienced boaters? Are boat carbs that much different than carbs on a motorcycle or a car? Is there any special thing to look while cleaning? I made sure to follow the cleaning process in the mercury 90 manual.

The mechanic did say something about balancing...which I do see as being a possibility as to why they aren't running correctly (but i do NOT think they are still dirty). Any thoughts? Can you balance carbs on the assembled engine or do i have to take it apart again?

So to update, i re-tore the carbs apart, cleaned EVERYTHING again, and adjusted one of the floats that seemed off per the manual...put everything back on except the intake and it seems to be running a lot better! i can actually put it in forward and it will run under power. The only thing i do notice (intake is off), is that once in a while the carbs do alternate spitting smoke under idle / a little flame under power. Could this be because i still haven't sync'd the carbs yet?