2017 Harris pontoon 115 mercury. Full tank each time use 1/4 tank -motor cuts out. 1st replaced plugs; 2nd occurrence-dropped motor; 3rd time plastic part replaced behind prop.Still occurs. Ideas?
I'll take a coupe of guesses at this :>) You have a fuel supply problem if the engine works fine until a certain level in the tank is reached. To me, changing the plugs and the plastic part behind the prop would have no bearing on your problem.
Are your fuel lines Ethanol rated and are you using ethanol fuel. Non compliant fuel pipe degrades on the inner walls enough to block or severely restrict flow.
Do you have a fuel filter? Is it clear and not blocked?
Check for a pinched pipe between the tank and the motor. I have one that will if I don't connect carefully.
Is the primer bulb in the right way round, arrow in the direction of the engine. Seen that a few times.
Finally, it is 2017, so the engine is still under warranty. I have a Mercury 60, and would suggest you take one or two years extended warranty after the first 3 years. I had a lower unit seal become dislodged at the end of year 2, I got it fixed before the warranty ran out. No problems since.