'97 Mercury 40 hp Losing Power

[nitramag]

I am trying to help a friend with a 1997 Mercury 40 hp (4cyl w/oil injection). He didn't use it for two years, so I had to rebuild both carbs to get it running. Now it starts easily and for the most part runs like a new motor. The problem is that the motor goes from full speed to idle after we hit a large wake. The engine loses all power but still stays running. During the loss of power it sounds as though it is not getting fuel and the rpms stay low. No warning alarms go off. The engine also runs very rough during the episode but quickly recovers. By shutting the boat off and restarting it or bringing the throttle all the way down it seems to fix it and the boat runs perfectly. Yesterday we ran the boat for about 30 or 40 minutes on smooth water until we hit a fairly large boat wake (his boat is a 17 foot aluminum fishing boat). As we were going over the second roller the engine lost power and went to idle speed. We shut down the motor and it instantly started and ran fine for another 30 minutes. We were able to reproduce this condition two more times by circling over our own wake.

I'm thinking that one of the fuel lines on the motor might have deteriorated from the Ethanol fuel and the bouncing over wakes aggravates the conditon and closes off the line. Assuming the blockage was past the fuel pump the pressure would keep the blockage closed until the motor was shut off and the pressure was relieved. But could a blockage shut down the motor that quickly? It usually dies as we are going over the second or third wave or roller.

Any ideas? I'm going to check the fuel lines as soon as I get some time. Probably later this weekend.

Thanks for your help.

 

[joed]

wild guess. Water in tank. stays below the pickup. wave sloshes it and the engine gets a gulp of water.

 

[nitramag]

Thanks Joed. He bought a new tank and primer bulb and filled it with fresh gas. The fuel line from the tank is at least a few years old. Probably something else I should check.