25hp Johnson High RPM Miss

[napaman2486]

This is my d'boggle. I am driving my self nuts trying to figure this problem out and the engine is teasing me after i make each repair. So.... I was finishing up a great day of fishing and heading into shore when my engine decided to mis-fire badly. So common sense tells you to let off the idle, which i did. It will run like a dream at idle and never die, and even run perfect at 1/4 throttle untill you open her up. Then it will will missfire. If i let it idle for a few seconds i can goose it to 90% for about 10 seconds and then missfire. I have read a previous forum on a almost exact problem but it was never finished. I have replaced plugs, wires, fuel hose, and 100% complete rebuild of the carberator. So i take it back out and she runs like a top for about 4-5 minutes then drops down again. I am thinking i am having problems with a coil or igntion control module heating up? Can anyone comfirm this? If so, please help i just want to fish and it doesnt help im surrounded by lakes (Minnesota) and mother nature has been messing with our weather enough lately.5 inches of snow on may 1st? come on please help

 

[bgbass.1]

Re: 25hp Johnson High RPM Miss

When it does it try unplugging the tan wire on back that goes to the temp switch it could be faulty and sending a false signal.

 

[jbjennings]

Re: 25hp Johnson High RPM Miss

I think you're on the right track with the coil or powerpack. What year is your motor? You might try waiting until it starts that missing real bad and pull the plug wires one at a time and see if it affects the running of the motor. If pulling one has no affect then the coil or powerpack could be faulty. Since it's only doing it at high rpm's it may be hard to diagnose. I've had it happen before like you described and a new coil fixed it. Those parts can be expensive so it's probably best to figure out how to test 'em. I'm not sure of the correct procedure.
Is it having trouble getting up on plane when it starts missing? If so, I'll bet you can catch it by pulling a plug wire and finding the dead cylinder.
Hope you figure it out,
JBJ

 

[napaman2486]

Re: 25hp Johnson High RPM Miss

Well The coil packs did not work, so i ordered in the power pack from my work for 50 bucks. There is no tan wire on this model i searched high an low and there is nothing? So i will reply after i throw the power pack in. thanks fo all the help guys