Yamaha 50 hp 4S F50TLRB #4 Carb Floods

[gchronister]

I bought a 2003 16DLX Carolina Skiff with a Yamaha 50 hp F50TLRB engine and it never ran quite right by popping on fast acceleration and a noticeable miss on normal acceleration. It has sat most of its life so I assumed it was a gummed up carb. It always noticed it had a miss and would pop and stall on acceleration. Carb rebuild time right? Yes, well after a full cleaning of all four carbs, #4 carb now FLOODS the cylinder and shuts it down after just one minute of running due to being too rich. Before it floods it runs strong and smooth. I had suspected the enrichers but I checked them by 1. disconnecting, 2. switching location. No help. I then swapped the float bowl and needle from carb #3 to see if the bowl was flooding. No help. My question is, what about the flat rubber gasket on the top of the carb. Could it go bad enough to cause a rich mixture. I will today try swapping the gasket with another carb and see what happens.

Any ideas? PS, the electrical system works great and has great spark on cyl 4 with new plugs. As soon as I clean the pulg when fouled, it will pick up the cylinder again but then flood it out after a minute. Please help.

[99yam40]

did you follow the service manual procedures to link and sync the carbs and fine tune them?

[rodbolt17]

it is simple.
fix the leaking needle valve.

[gchronister]

Not so easy

Yes, I sync'd the carbs and I changed the needle and float. I ran the engine and now all cylinders are showing fouling. I just talked to a Yamaha mechanic and he believes the the fuel pump may be drawing in oil. I think that might be right, so I will change the fuel pump diaphragm to eliminate that issue.

Also I ran the engine without the air horns and there is no sign of excess fuel flowing from the main nozzle. I will let you know after I fix the fuel pump diaphragm,

[rodbolt17]

if the oil is not contaminated with gas you can rule out the pump. however it is always a good idea to at least inspect the diaphragm when you do the carbs.
have you done a leak down test?