'91 Mercury 175HP - Place in gear & she shuts down

The gearbox is fine. This started happening all of a sudden - I turned off the engine to pick up a skier, then upon restarting (difficult), the engine idled erratically, then shut down upon placing it in gear. Now a weird thing about this is that we pulled the boat out of the water and with ears on it, the motor started and ran fine. We put it in gear and it instantly rev'd to full throttle when called for. . . We placed it back in the water and it ran for maybe 15 minutes, then the same thing. Carbs were rebuilt less than a year ago. Plenty of fuel appears to be getting to the carbs. Pumping the bulb does not appear to help. Ignition module was replaced about 18 months ago. What else could it be? Thanks!

Re: '91 Mercury 175HP - Place in gear & she shuts down

Do you have a water seperator on that motor? It sounds like a bit of water in the fuel, or some dirt in the carbs.

Re: '91 Mercury 175HP - Place in gear & she shuts down

Hi and thanks for the reply!

No - I don't have a water separator on it; though, we did drain all the carbs and capture the gas from them into a clear container. I couldn't see any sign of water in the container; though I was really hoping to see some; thus, I'm not sure about water in the fuel. Whatever else may relate to a carb issue, it doesn't appear to be stuck floats or debris (at least through the float valves).

The description sounds pretty-much like a fuel issue to you??

Re: '91 Mercury 175HP - Place in gear & she shuts down

Every boater today should have a water separator on their boat.. I have 9 boats and everyone has one..My 19ft Daytona has a water separator on each tank and a racor water separator before the engine..Don't want to lose a $10,000 outboard because of water...Chalk it up to Ethanol..Google it and read what it does in our boats from sitting....

Re: '91 Mercury 175HP - Place in gear & she shuts down

Yes, it does sound like a fuel issue to me. Ethenol can mix with water to produce lousy fuel. Usually it gets cloudy when mixed with water. Did you see any of that in your carbs or tank? Premixing oil with the gas makes the cloudiness easier to see. I don't know if you have oil injection on that motor, but if you do, add some oil to the fuel you are testing for water.