F50aet problems

[nauticaowen]

Hello everyone, my name is Owen, i was trying to find a section where introduce my self and say hi at you guys but i couldnt find it. Im from South America, Patagonia Argentina. First of all, i will do my best to express my self good as possible because my english may not be the best!
Because we are a 1000mi from a "possible solution" from a oficial dealer, my friend and i decided to try to find out whats going on with this engine. Im dealing with a yamaha 50 in line 4 cilinders 4 carbs F50AET. The engine shows 308hs in the tach. First impression was engine running rough and testing cilinder number 1&4 having spark but pulling out the sparkplug cap nothing happens on both. I did the following:
1)test and change sparplugs and wires = nothing.
2)invert ingnition coils = issue persist on same cilinders instead of 2&3
3)check fuel pump =spits like hell but anyway i pumped fuel manually and nothing.
4)with cold engine i check valve clearance = all in good values
5)warmed up engine, check compresion, its perfect almost 120psi the four cilinders.

The next thing i did brings me as result to become crazy:

6)pull out all carbs, check filters and i do an exaustive check an cleaning with compressed air and carb cleaner. As result, engine runs perfect, i took the boat to the water, runs perfect for a while but suddenly starts to fail again.
First thing i guess was dirt comming from the tank so i took out AGAIN the carbs, first impression remains cleaned, cleaned all again, reinstalled them and issue persist.

Last night i couldnt sleep thinking what i have been missed to check.- Im thinking if theres a chance to be a CDI problem...? how do i check it?

Thanks everyone!

Owen.-

[nauticaowen]

7) Inyecting fuel via the intake manifold the cilinders runs so i guess it may be a fuel problem but reclean carbs and nothing happends.-

[rejesterd]

If cylinders 1&4 are still not firing now, it's surprising that cleaning the carbs made it run better for a short time. When the same 2 cylinders are consistently not firing, it's hard to assume that the problem is fuel-related. So I'm not sure what to think about your results there.

The only clear thing is that cylinders 1&4 have a problem firing. They are linked by the same ignition coil, but you swapped them already. The only other thing that links them is under the flywheel, there are 2 protrusions for timing: one for cylinders 1&4 and another for cylinders 2&3. Maybe the one for cylinders 1&4 is damaged or loose.

[99yam40]

7) Inyecting fuel via the intake manifold the cilinders runs so i guess it may be a fuel problem but reclean carbs and nothing happends.-

well if spraying fuel into the intake makes those cylinders to fire ,you know for sure it is a lack of fuel.

I thought the 4 stroke motors had more compression than 120psi,
I would expect 120 from a 2 stroke motor.

sounds like you need to use a heated sonic cleaner maybe, or soak the carbs in a carb cleaner, and then blow compressed air thru all passages
make sure you take them all apart when doing this.

also make sure you follow procedures in service manual when setting the carbs. will need a 4 channel vacuum gauge made for setting them

[panasonic]

This is one of those over complicated F50 four carb setups.

What is all the information on the data plate? Serial number and stuff. Trying to figure out the motor year.

Was it not Chuckb1954 who just when through a complete carb ordeal on one of these???