2001 Mercury 4 stroke will not go to full throttle

[Hpracer]

My 115 horse Merc outboard starts and runs great at low speeds and all the way up to about 3/4 throttle between 4000 and 4500 rpm. The gas was treated over the winter and the external fuel filter was just replaced. The fuel filter inside the cover was removed and checked without anything being wrong. The motor runs without missing a beat up to 3/4 speed but when I go for full throttle I initially get that woop that you hear at WOT but then it stops and the motor doesn't want to go any faster. It seems like something is cutting in and keeping it from going higher rpm.

​Is there any kind of a governor that would allow 4000 to 4500 rpm but restrict it from going higher? Anything else I should check for? We have tried squeezing the bulb when this happens and there is no improvement. The VST has recently been checked and nothing was found, and the injectors were just cleaned last year. Any help would be appreciated.

 

[Texasmark]

Get a wiring diagram. I'm assuming from what you said that you have a defective "over revving module", assuming the engine has one.......not familiar with 4 strokers but when you said it would rev ok for a second then drop back that sounds like a sensor reaction and the actual numbers it sees are not what it thinks due to a component internally changing value.

 

[Hpracer]

Well, I went to our local Marina and talked to one of the knowledgeable mechanics that has my same motor, and he thinks it is the screen in the bottom of the high pressure fuel pump located in the VST. I said that I had this apart recently but apparently not recent enough. This guy says that he takes his apart three times a year to clean the screen, that even a minute amount of corrosion and a slight clogging of the screen is enough to keep that particular motor from running WOT because it has a tiny screen. He also said that if the gas is a couple of months old you should drain it and put it in your car or truck, because it can pick up moisture and with the ethanol gas can eat away the inside of the VST and cause corrosion which will clog the screen.

​Maybe a topic for another thread, but does anyone know of a coating that can be applied to the inside of the VST to keep it from being attacked by the acid formed when the water in the gas combines with the ethanol? That VST is $375 just for the bottom part, and this will be the second one that I have had to replace in just a couple years.

 

[Texasmark]

Might add some Sea Foam to the gas. It has mineral oil which can coat the screen, and naptha and alcohol to keep things cleaned up. It's a fuel stabilizer also. Info and directions on the can.....ww sells it for $6.50 a pint here.