Cant throttle motor above half throttle or the motor dies. 77 Johnson 115 HP

by Jeremy
(Casper, Wy, USA)

My brother has a 1977 Johnson 115. We have been working on this motor all summer long. There are times that we get the motor to run 100% great. top speed of 34 mph. then 85% of the time it when we try to throttle it up above 1/2 throttle it wont do anything other than die. It will idle fine and low speed it seems to be running good but anything above the no wake zone and its almost like its afraid of the deeper water lol. We have changed the fuel lines, primer bulb, filter, and rebuilt the fuel pump. We have also installed a new impeller and changed out the gear oil in the lower unit. Still no change. It runns great on the muffs but as soon as you get it int he water problems occur. The exhaust relief ports do have water coming out but only enough to create drops on your hand. We took it into a boat shop recently and they are telling us that there is 87% leakdown on cylinder 4. Im not sure to believe this or not due to the fact that we can get it to run sometimes just fine. Can anyone help me here?

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