Yamaha 50 HP not running at high speeds, sputtering/hesistating/missing

[gobucs1]

The outboard is only running at about 1/2 throttle smoothly and any more it hesitates/misses as shown in the video where 1/2 throttle is the max speed I can go. The boat can get on plane and that's about it.

Engine is Yamaha DETO (European model?) 50HP 1984 or 1985 model

Compression is 120-120-120 with spark on all 3 cylinders.

Plugs were just replaced when this first happened, still look good last night. I have done three trips out like this to empty the fuel if it was bad gas but I use ethanol free gas and it never sits long.

Any suggestions of what to look at? or what other info is needed? Even describing the symptoms I may be off but the sound in the video is the problem. I will replace the fuel water separator tomorrow evening as I still need to buy it.

Thank you for any ideas and help!

In the video you can hear the sound of the motor when I accelerate change to the problem hesitation/missing. This is what needs solved. (skip ahead to 20 seconds)

http://vid957.photobucket.com/albums/ae59/ufgators1/Mobile%20Uploads/20150729_134252.mp4
Copy and paste into new window and this link should work.

 

[robert graham]

In 30 years have the carbs ever been removed, disassembled, cleaned, re-installed and set?.....you may have plugged carb jets

 

[gobucs1]

Yes last year they were taken apart and cleaned and I replaced the gaskets and cleaned the jets. I took them apart last night and removed all of the jets and cleaned again. Nothing looked bad and no debris was visible in any of the carbs. I will run it again this weekend to see if any difference at speed.

 

[99yam40]

check fuel pump to see if it is leaking into the crankcase and causing #3 cylinder to not fire properly/
A spark tester or a inductive timing light should show if plugs are sparking.
Check to see if timing is advancing as it should

 

[gobucs1]

check fuel pump to see if it is leaking into the crankcase and causing #3 cylinder to not fire properly/
A spark tester or a inductive timing light should show if plugs are sparking.
Check to see if timing is advancing as it should

I ran the motor last night and advanced the throttle while in neutral and it still has the problem at high speed.

To check the fuel pump leaking would I remove two screws that hold it to the motor while leaving the other screws to keep the pump together. I would then squeeze the primer bulb and see if the pump leaks fuel?

How would I see if timing is advancing without a timing light?

 

[Propwash79]

I just had the same issue with my 1996 suzuki dt 40 and rebuilt the fuel pump.i would su rebuild it cause it has some age and see if that makes it better.

 

[99yam40]

timing light is needed