1990 15hp Johnson - fouls plugs?

Dave Diefenderfer

Dave Diefenderfer

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I have fouled 2 sets of plugs in less than 10 hours of run time. Using the stock plug number, NJK brand. Should I go hotter? What indicates a hotter plug? Using 50:1 mix, less oil? What else should I think about? Change plugs and it runs great for a few hunts, then they go bad.

Dave
 
I'm no expert... you get what you pay for here :) My 25 fouls badly when idled extensively. Many of my hunts I barely ever get over half throttle. The 50:1 mix rate is for WOT. Mixing less would work but it opens up other potential problems. I'd probably try a hotter plug. My solution has just been to use the warm up lever and high idle a bit or if somewhere possible take her out for a nice little run.

Gene
 
Rich, The first number is gasoline not oil. 25:1 would be more oil for the same amount of gasoline. Less oil would be something like 75:1 which is not enough. Do not experiment with oil ratios. 50:1 should be right. Also I have found that NGK as less likely to foul than sme of the other brands. Make sure you have fresh fuel, old fuel may not be burning right. I am kinda supersticious (sp) about oil and ussually use brand name oil. Don't want to start a peeing contest over oil but some are better than others. Also do not experiment with heat ranges of plugs, too hot a plug can holea piston. Hotter plugs are not the answer to fouled plugs. Maybe one heat range hotter but not any more.
 
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Dave,

I suggest you review some of the info available on NGK's web page. Lots of good information on plugs and such.

It may be more of a too rich fuel mixture problem rather than too much oil in the mix.

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Change plugs and it runs great for a few hunts, then they go bad.
Click to expand...

Not really, new plugs don't "go bad[/font]" after a few hours of run time. Even if they get carbon fouled they are still not "bad" just dirty and fouled. They can be cleaned up just like new, using tools you probably have on hand.

Step #1 heat the working end up with a propane torch to a temperature of between 500°C (932°F) and 800°C (1472°F). The carbon fouling will burn off leaving a tan to white ash.

Step #2 use your air compressor and a toothbrush to clean off the ash residue.

Now those plugs should be good as new.
 
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Good point Dave, I have found in the motorcycle world if you just get out and run NGKs hard they tend to clean themselves up better than most other brands.
 
you might want to check carb adjustment. not knowing how you drive boat (let idle when putting dekes out or long ride at idle) your low speed jet adjustment mite be to rich. to much fuel and oil going to chamber to be burnt that fouls plugs hope this helps you out
 
My old 71 6hp rude did the same thing after I took it out of mothballs. Best thing I tryed was Lee's fav. fix Seafoam, I ran a couple tanks strong with that stuff & it ran a lot better. Before I left it running setting & picking up at an idle, it sputtered, backfired, died a lot& crudded plugs. By the end of last season it was a different motor, ran great& plugs lasted all season. I don't know whats in that stuff, but I now know why Lee loved it.
Dennis
 
Try champion plugs if the NGKs aren't working out, Champions alot of the time will run better in johnson/evinrudes than NGKs.

I have a 15hp yami, and they have switched over to recommending 100:1 in there small 2 strokes, i run somewhere in the middle around like 80:1 out of fear haha.
But since i've made the switch from 50:1 i stopped fouling plugs. I dont know if J/E have changed .... I would try the Champs as an inexpensive experiment..

goodluck Dave!


Dan
 
Oil mixture shouldn't foul the plugs unless you're running 25:1 or more.

Low speed mixture can foul plugs when the motor is run at idle/low speed for extended periods. On a 1990 Johnson you should have a mixture knob. Pull off the knob and turn the mixture needle all the way to the right until it stops, then back out 1 1/2 turns and reinstall the knob. This will reset the mixture.

If the plugs are still fouling, you can try a hotter plug, but it does not solve the problem. Carb may need to be rebuilt, especially on a 1990 motor (if it has never had it). Reed valves may be fouled as well.

Everything can be traced back to Ethanol in the gasoline. Ethanol eats away at materials that weren't made in the ethanol era. In other words, a 1990 outboard should have all fuel lines replaced with newer lines. Fuel pump can get eaten alive too by Ethanol. This can cause debris in the carb, poor fuel delivery or even too much fuel delivery. I would try and solve the problem, rather than switch to a hotter plug.
 
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