2003 Mercury 90 outboard (4 stroke) running rough, wont idle

[audiocontr]

Engine has 200 hours. Worked fine a month ago, start it now and find it running VERY rough. Wont idle. I swapped out the gas and noticed the carbs bowl gaskets were leaking. Replaced all gaskets in the carbs, new plugs, still wont start and run unless i have the accelerator turned up. sputters and pops

Compression shows 175 on 1, 2, and 3. 150 on 4. I'll check the valves after it cools overnight

The engine drops equally when i pull a plug wire across all 4 cyls

Any suggestions of what to look for?

 

[ondarvr]

You replaced the float bowl gaskets, but did you thoroughly clean the carbs?

 

[audiocontr]

Yes, carbs were in great shape, but sprayed with cleaner and blew out with air. Idle screws were a little gummy, but otherwise in good shape.

 

[audiocontr]

quick question - which way does the one way vacuum diaphragm point on the lower carb? One side has a ridge, and by the looks of the diagram, it points toward the carb. is that correct?

 

[audiocontr]

It was the check valve. Back to running. Still a little rough so looks like I'll sync and tune