25 Johnson high end miss

[Cedarridge]

I am not sure of the year 89 I think. Model # J25ELCEB, ser # R 08170921. Please help. This motor is a very strong running moter until recently. It idles fine, slow speed is fine, 3/4 speed ok, wide open it starts to miss, cough, and sputter, and once even it kicked up out of the water as if I hit something. I can then idle down go slow for a few minutes and go again. Weird. I did take it to someone who does boat repair, he first said it was the water pump 182.00. Of course the next time out on the lake it did the same thing. I then took it back to him, he then ran it out on the lake was able to recreate the problem and said it must be one of the coils, he ordered the part but did not install it. He said that he recently spoke to another repair man and they told me that I should change my prop because the one that I was using was putting too much of a load on the motor. This does not make sense, because it has been running fine for years. Any ideas, I want it to run without costing an arm and a leg! Thanks.

 

[HighTrim]

Re: 25 Johnson high end miss

To start, Im not real sure what a faulty waterpump would have to do with your symptoms. Not to say that it wasnt needed, but I would question that further. Did he check to see if you were losing a cylinder at WOT? What is your current WOT RPM?

Backfiring out of the exhaust is caused by having the ignition system fire a particular cylinder when the exhaust port is open ( ie piston down). This would sound like a shotgun going off..... is this the condition that you're experiencing?

This is usually due to a sheared flywheel key, a flywheel with melted (moved) center sensor magnets if they exist, timer base leads routed incorrectly to the powerpack, or having the leads from the powerpack to the coils reversed to mention a few.

Spitting back, sounding like a mild backfire, indicates a carb restricted jet..... something causing a lean carb scenario.

 

[AlTn]

Re: 25 Johnson high end miss

if you'll take an inductive timing light and check each cylinder when it's "cuttin' up"...you can determine if it's an electrical problem or a fuel side problem...just look at the strobe light and you'll see no spark, or weak spark flashes..if no changes in strobe frequency or brightness..you could still have voltage leakage in the sparkplug boot area or just a sparkplug itself breaking down...anyway...it's a starting point for electrical issues..fuel side, I'd take a spray bottle with fuel mix in it and spray it in the carb throat at wot if the motor passes the electrical test...if the fuel mix spray gets it to running "well" again even for a moment...the fuel side of things needs addressing

 

[234rick]

Re: 25 Johnson high end miss

Coil wire seperating when opened up( where it enters the timing plate).