2000 F115 Power Loss

My Yamaha F115 experiences power loss and sputters only when warm. When cold, the motor has plenty of power throughout the RMP range. After 5 minutes of water skiing, the motor sputters and spits after throttling back to idle, and then kills most of the time. It then starts easily, but runs roughly at idle for a minute or so before idling smoothly again. But all is not well at this point. When attempting to pull up another skier, the motor has significant power loss, to the point of not getting up on plane. If I let the motor cool for 1/2 hour, the power is restored. There are no heat alarms or forced shutdowns issued.

History:

I had an overheat alarm 5 years ago and replaced the impeller and thermostat, which fixed the alarm condition.

The peehole is running with good pressure.
I pulled the thermostat and it performs to spec
I pulled the water temp sensor and it performs to spec
I have changed the water fuel seperator
I have changed the external fuel filter

Any ideas?

Mark

Re: 2000 F115 Power Loss

I had the near identical issue with an older Johnson motor (I'm only checking the Yamaha site as I'm looking to buy a boat with an F115). For my issue, it was a matter of cleaning the fuel path from build-up and had nothing to do with temperature. I believe it was from the debris/build-up loosening as I ran the motor for 5-10 minutes and then I would have all kinds of hesitation until I let the motor sit for a while as all the junk settled.

I did not have an EFI, so the path to fixing the problem was through a full carb cleaning (In one later case, a jet came loose -my mistake- and plugged up the fuel path causing the same issue), but I assume the issue would be in build up before the injectors in your case (post external filter).