I have a 75 Johnson 50 horse that just starting having RPM problems. It will start and idle fine. It will also run fine at WOT for about 20 to 30 seconds before it starts to "die down." If I leave the throttle at wide open, the motor RPM will fluctuate smoothly back and forth like someone is playing with with the throttle. If I pull the throttle back between 1/4 and 1/2 throttle, the motor will stop fluctuating. As soon as I go to WOT, it starts acting up again. If I stop for a while, and let the motor cool, I can get it back up to WOT, but the whole process starts over again. So, it's almost like the problem starts when the motor gets warmed up. I have changed the plugs (thought I might have fouled one), cleaned the carbs, and also tried to pump the primer bulb while operating at WOT. None of this has worked. Does anyone have any suggestions?
