2004 F115 Yamaha Hesitates

Greetings,

F115TXRC began hesitating this season. Here's the background:
- Approx 50 hours total time.
- Runs <10% ethanol 87 octane.
- Built in tank (Hurricane 187) always kept full, with Stabil.
- Engine ran fine last season.
- Installed Sierra water separator filter prior to first operation this season.
- About 30 minutes into first op this season, engine began running rough.
- I emptied entire tank and refilled (added Lucas cleaner).
- Discarded fuel appeared clean (debris and water free).
- Sierra filter was clean, as was engine mounted filter.
- Replaced plugs.

Subsequently, engine idles reasonably well. In neutral...
- - Throttle burst from idle is fine.
- - Throttle burst from 2000 rpm has momentary hesitation.
- - Engine doesn't want to stabilize between 2200 and 2800 rpm (slow
throttle increase above 2200 yields no increase in RPM , then jumps to
2800. Slow throttle decrease from 2800 suddenly drops to 2200.)

Generally, engine runs smoothly at higher RPM. Yields 5800 RPM at WOT, 46 mph more or less.

Any ideas? Thanks from St. Augustine!

Re: 2004 F115 Yamaha Hesitates

I had this problem 2 seasons ago. Had a small area where it ran rough, stumbled. Engine purred below and above the rough area. The next season, major issue.

Here is what my rough spot turned into and what you may want to do now and not wait.

http://forums.iboats.com/showthread.php?t=244492