Hey there I've been reading here for a long time, but finally have a problem I cannot solve by reading old post. I've been in the process of bringing a 1975 25hp Johnson back to life and am having problems. It was my grandfathers boat and ran fine prior to sitting for 15yrs. First I will list what I have done to the motor. I have replaced: all three coils, points and condensors, fuel pump and lines, spark plugs, impeller and thermostat along with rebuilding the carb. I have been testing it in a trashcan in the yard. It will fire right up and idle smoothly, and without the prop on it will rev up to full rpm no problems. However when on the water it will only run at what i would guess is 25% of the rpm it should turn at full throttle. The throttle plate is fully advancing, and the butterfly is opening all the way on the carb. I know that the main jet is clear and the float is set correctly on the carb. It runs smooth, not bogged down and no excess smoke, it just will not turn up and make power. Also pumping the primer bulp on the gas tank has no affect on how it runs. Any thoughts would be appreciated, I've done everything I can think of. Sorry for the long first post..
