50 HP Johnson high speed issues

[ttirb]

My 85 50hp Johnson loses power momentarily above 1/2 throttle. It is as if it loses a cylinder for about two seconds then surges back and runs correctly. I have rebuilt carbs/fuel pump etc. Engine cranks, idles, accelerates and runs smoothly. I believe this is electrical since it seems to be erratic in nature. Have checked spark gap, plugs are correct, wiring looks good, connections are good. I suspect coils or power pack. Any suggestions or similar experiences ?

 

[HighTrim]

Re: 50 HP Johnson high speed issues

Does this usually happen between 2500 - 3000 rpm?? Make sure you're not overheating. Disconnect the tan temp wire from the pack and retest.If the engine now runs properly, replace the tem switch.Make sure the tan temp switch wire is not located next to a spark plug wire. Im not sure, is your motor a 2 cylinder CD Ignition?? If so, check the DVA output on the orange wires from the power pack while connected to the ignition coil. You should have a reading of at least 150 V or more, increasing with engine RPM until it reaches 300 -400 Volts. A sharp drop in voltage right before the miss becomes apparent will normally be caused by a bad stator. A drop on only one orange wire will normally be the power pack. Check the stator resistance. If is reads approx 900 ohms, replace it with a 500 ohm design.

 

[ttirb]

Re: 50 HP Johnson high speed issues

Not getting hot, checked with infrared and running about 165-170 at the hottest spot. Does the voltage check need to be done under load ?