posted 07-19-2004 08:24 PM ET (US)        

The motor seemed to perform OK at idle and moderate speeds, but much above half throttle and the motor would seem to starve, and would die, like right now. Seemed like either an air leak, or a fuel filter problem to me, and since I knew (re-checked anyway) that there were no air leaks in the fuel system, I removed the canister type Mercury fuel/water seperator, and did find about 1/2 cup of water and some gunk. I'm not familiar with the canister types, being used to Racor filters where I can drain water out of the bottom, so I refilled the filter element with gasoline and dumped it a couple of times hoping that I would thereby get rid of enough contamination so the motor would run OK.

It didn't run OK and in fact over a couple of hours of further messing around, changing out the secondary fuel filter, etc., it finally wouldn't stay running at all.

I'll only post the short story here without all the details about using more than 15 gallons of gas (and nearly running out)running from a portable 6-gallon tank into town 8 miles away by water and the towed return boat breaking down too, or the fact that I had to wait while the Marina that had just picked up the Yamaha dealership in that neck of the woods developed their on-line capacity to download the Yamaha diagnostic data before they could run tests...

Bottom line is they eventually diagnosed a bad (failed) diaphragm in the middle (of three) fuel pump. Had to order it in overnight from Hodunk or somewhere, but that was the culprit, and everything seems to be back to normal.

posted 07-20-2004 03:39 PM ET (US)         

Sorry to hear about the fuel pump, about which I know nothing on Yamahas. But do know that EFI engines are extremely susceptible to water in fuel, hence the secondary engine mounted water separator. My Mercs have an alarm on the under cowling filter if it becomes filled with water and needs replacing.

You might try to determine where all the water came from.
Is the boat tank kept full after about Sept 15th and through the winter? Try adding some MDR "Waterzorb" (contains no alcohol) to the tank also, and especially for the winter.

Also always keep a spare Merc primary filter, and Yamaha secondary filter, on hand.

posted 07-20-2004 04:06 PM ET (US)            

We're back home now, licking our wounds...generator trouble (I now know more about Cummins stop solenoids and the profit Cummins Canada feels required to make on them as opposed to that which Cummins USA needs to make than I ever wanted to know), propane refrigerator trouble (ho-hum), Yamaha trouble (already discussed), and Montauk trouble (failed key switch - couldn't diagnose at camp, but was fairly quickly done at the Marina). You should see that Montauk now that I'm done with it though.

I do carry a spare Yamaha secondary filter, and *should* carry a spare Mercury water/fuel seperator cannister - don't know why I haven't - I will do that now...