My 2001 Vmax 225 EFI started to make an awful knocking sound. It has made a few odd sounds over the last couple of weeks when idling but a Yamaha tech told me it was most likely engine knock from ethanol. He said that the most important things to do are use an ethanol treatment and install a water seperator filter. I had already done both earlier this year (I uae Stabil Ethanol treatment and I installed a Yamaha 10 micron water seperator filter).

I was out pre-fishing for a tournament yesterday and I was moving around quite a bit looking in different areas, sometimes at lower speeds and sometimes at WOT, as usual. Everything was normal yesterday until my last move of the day. I ran about 2 miles at near WOT and as I started to slow I heard an awful knocking sound that would not go away.

The sound is constant but it is a higher pitch when in neutral. It is still there when I put it in forward or reverse, but it is a lower pitch. The motor performed normal and I made the trip back to the launch without any problems. Once it was on the trailer I took the cowling off and fired it up again (in the water) and I could feel the thumping when I touched the flywheel, etc.

I can't imagine that a sound like that is a minor problem, but like I said, it continued to perform normally at various RPM's/speeds on the way back to the launch. All feedback is appreciated!!