I put it in the shop... had service done, oil, oil filter, lower unit serviced, fuel filter, plugs checked.
Computer hooked up with no codes showing up.

Burned fuel down to 1/4 tank, filled tank, in order to have as few
Additives in gas as possible...had recently ran Seafoam and Heet
In previous couple of tanks.

Today would run about 3 miles at 30+ mph when motor would start cutting out,
If throttle increased it would cut out worse, if reduced to 18 mph, no cutting out...or, if throttle moved to
Neutral for just 10 seconds, motor would run like 3 more miles before cutting out...move to neutral
Again for 10 seconds, good for another long run.

Emptied water seperater filter before last fill up, could see about three tiny drops of water
In jar. So, added one bottle of Heet to current
Tank of fuel.

Try checking the fuel lines. Start at the tank and work your way toward the engine. I have seen pin hole leaks in every part of the fuel line and they all cause similar problems. It's usually the primer bulb or the quick connect fittings. Hope this helps.

Forgot to mention there is a 19 gallon tank and I run through 12-15
Gallons per week

Three year old motor

Sounds like a fuel line problem to me. Maybe collapsing inside, a pin hole or...... just not picking up enough fuel at high RPM's. Hope its a simple fix.

Check the fuel line going the coupler at the front of the cowling. Have been seeing a lot of problems with the grey fuel line on these Mercs. The 4 strokes are also having a lot of problems with the float in the fuel supply module. Some it is necessary to replace the complete fuel module. Have also had problems with the fuel demand valve between the tank and the motor.

Today

Ran 3 miles at 30+ mph
Fished
Ran 2 miles
Fished
Ran 2 miles
Fished
Ran 2 miles fished
Ran 3 miles to marina

Never cut out

Thanks to everyone for your help.

I ended up cutting out until I used gas level down to less than a quarter.
Filling tank diluted any fuel additives I might had built up in the tank.
Then, only additive I put in was Heet.

I then ran three days in a row with no motor problems. Added more gas to tank and have now run three more days with no problem. Hopefully fuel was the only problem.

Thanks again

Your fuel pump could be going out. Low fuel demand, no issue. High demand, cuts out. Intermittent for months and months. Replaced fuel pump, problem gone.
Tim

This thread was started back in July. My motor had been cutting out since April. I had it in the shop twice and both times put on a computer, with different adjustments done to the motor.

I hooked the motor to a separate fuel tank and it still cut out. I changed the hoses.

Finally I learned that hooking a Mercury to an aftermarket computer will not read all codes that is being thrown by the motor. So we hooked it to a Mercury computer and it showed

LIAC_OutputFault with a stall motor.


Mechanic figured the shift sensor was sticking, causing the motor to think it was in neutral and thinking it was going too many RPM for neutral.

He replaced the Shift Sensor and it appears the problem has been fixed. Maybe this will help anyone else that might have a similar problem.

Collapsing fuel line. The interior lining in the hose has come loose. Ethanol is tough on the older fuel hose.