Yamaha 50hp lose of power after 10 minutes

[Julian Smart]

Hi
I have a 1997 50 hp yamaha will run great for about 10 minutes then will loose power stale and not really start again if it does as soon as you put in gear it stops and sounds rough when in neutral. If you remove cover and leave for about 10 minutes it will start, but difficult to start, then go again for 5 minutes then same again. Have noticed a couple of things but not sure if significant. After driving for 2 minutes with loss of power the bottom plug was wet and other two were dry, could third coil be breaking down under heat? Also on one occassion it went great and only lost power after going to tick over then would not open up again with out stopping when put under load.
Have fitted new plugs, cleaned carbs out, new fuel,
I am thinking its possible electrical?
Any input would be graet as its a bit fraustrating.
Many thanks

 

[Ray Neudecker]

Re: Yamaha 50hp lose of power after 10 minutes

The three cylinder engines have suffered from CDI failures. They have resulted in cylinders intermittently not firing. Take a timing light or spark tester and check for fire on all cylinders when it acts up.

 

[Julian Smart]

Re: Yamaha 50hp lose of power after 10 minutes

Thanks for that have tried on the drive and they all appear to be sparking but really need to try on water will do that Sunday.
Not convinced its not fuel related, does anyone know if they ever suffered from fuel pipes internally breaking down or being sucked in. Also anyone no anything about ultasonic cleaning of carbs, can you use the systems used for jewllery are the good enough as i am thinking although carbs look clean by eye they may benefit from a proper clean up

 

[Ray Neudecker]

Re: Yamaha 50hp lose of power after 10 minutes

There is always the possibility of a needle sticking intermittently causing the problem. If it were a V_4 or V-6, the fuel system would be the most likey cause. I have no experience with the jewelry cleaning process on carbs.

 

[Julian Smart]

Re: Yamaha 50hp lose of power after 10 minutes

All sorted now, took carbs off,stripped down and gave them a good clean with carb cleaner and now running great.
Thanks for the advise