1994 Johnson 40 runs terrible at WOT

I am new here and hoping you all can help. My father gave me his boat that has a 1994 Johnson 40 on it. He bought the motor new and had them disable the automatic oil mixing on it and he has always mixed the oil and gas.

The boat idles and runs fantastic at idle and low speed. When I try to go above 3/4 throttle the boat takes off like a scalded dog and may run good for a minute or two. Thats when it starts sputtering and losing speed. Backing the throttle off half way will allow the motor to run good again. It acts like it is starving for fuel at wide open. Dad took the thing in last year and they replaced something in the electrics and charged him $300 but it didnt fix the problem. Unfortunately he didnt get the boat back out so he didnt know the problem wasnt fixed.

I am thinking it is a fuel issue. If I leave if wide open and let it sputter long enough it will sometimes take off again for a few seconds before puking again. Almost like it uses up the available fuel and starts sputtering until it is able to draw fuel again. Im no mechanic but this is what it acts like to me.

I did a lot of reading here before posting and it looks like I need to try and pump the primer bulb when it screws up and see if that helps. I am thinking I need to inspect the fuel pump and possibly rebuild it. Could I just wire in an external electric fuel pump?

One last thing....the alarm buzzer in the shifter is dinging like crazy. When they did away with the automatic oil mix they told Dad that the dinging wouldnt hurt anything if he could deal with it. Dad is hard of hearing so it wasnt a problem but it drives me nuts. Any way to shut this thing up?

Thanks for any thoughts you can share.

Just to be clear, are you telling me to pump straight seafoam in the carb, or seafoam treated gasoline?

Thanks

I did open the cap on the gas tank thinking it might be a vent issue but that didnt help. I didnt notice the primer bulb collapsing nor have I attempted squeezing it when the problem shows up. Thanks again for the input.

I think you need to deal with / determine why the alarm is going off !!!--------Is it because oil injection wires are not disconnected ??------Is it because the motor is running hot and going into ----SLOW---mode to try and protect itself ??------------FIND OUT !!!

So are you saying these motors are equipped with some type of rev limiter if they detect a problem? I have a hard time imagining that the motor is running hot as there is great flow coming out of the tattle tale hose, but then again, Im not a mechanic. I would love to try disconnecting the oil injection wires to see if that silences the alarm but I havent a clue where I would do this.