1990 Johnson 15HP. Why would I be going through plugs every other outing?

[btkees]

So, I have had to change my spark plugs twice in the last month. Thats only two outings, not much running around. The motor would run good on our way out, on the way in, not output what so ever. Finally got it trailered, pulled sparks plugs only to find them scorched. Kinda lost what would cause this frequent event. Thanks in advance for all assistance.

 

[racerone]

Something is wrong.----What do you mean by " scorched " in this case.----Has the water pump been looked at ?---Are you running with a 50:1 gas / oil mix?

 

[btkees]

The internal parts of the plug, the ceramic and core are pretty much deteriorated. I do mix 50:1 and I rebuilt the water pump I have good water discharge. I don't see why they'd be getting so hot.

 

[racerone]

Thermostat checked ?----Plugs should last for years.-----Salt water motor ?-----Good pee stream does not automatically mean proper cooling.

 

[oldboat1]

water discharge meaning the pisser? You need some simple checks for overheating (heel of your hand on top of the head, IR temp gun). Look for paint scorching around the cylinders. Don't run it above an idle to test, and shut it down if it hits 160F (too hot to touch).

Thermostat issue possible, blockages, particularly if a salt water motor.

 

[btkees]

Well back to the drawing board. Got new plugs... I have no spark...

 

[oldboat1]

confirmed no spark using a tester? Be a good idea to run a compression check as well, as sounds like potentially serious overheating.

 

[Chinewalker]

What plugs are you running?

 

[oldboat1]

Chinewalker makes a good point. Recommended plug (Champion line) is probably QL77JC4.

 

[fhhuber]

Bad timing can chew up plugs and the pistons....

Picture of the bad plugs would help diagnose.

 

[Vic.S]

Chinewalker makes a good point. Recommended plug (Champion line) is probably QL77JC4.

Yes they are the recommended plugs ( gapped at 0.030") Alternatives are L78V (surface gap) and QL82C

 

[F_R]

Hm.m.m.. Burned spark plugs, assuming they are the correct plugs, are one sign of pre-ignition. And that can be caused, among other things, by too much spark advance. Now I'm wondering if there is a relationship between that, and sudden loss of spark. Sounds mighty suspicious.

BTW, pre-ignition can, and often does, destroy the pistons. Better make sure they are not damaged and find the problem before running it any more.

 

[fhhuber]

Its all meaningless speculation without a picture of the plugs.

A picture of the plugs could easily result in a definitive answer.

**************

And yes... I have seen silver dollar size holes blown through pistons by pre-ignition and I know what the plugs looked like from that engine.

 

[racerone]

Flywheel key checked ?

 

[F_R]

Flywheel key checked ?

Hey, good thinking. That could throw it out of time, and if off a lot could cause loss of spark.
btkees, remember to tell us what you find.

 

[racerone]

It will throw it out of time yes.-------It can be way out but you will still have spark.

 

[kbait]

If key is intact, you likely have a bad UFI (under flywheel ignition). OMC tried combining the CDI box (normally mounted to block) and the sensor coil (that's under flywheel) into one unit mounted under flywheel. They switched back after a couple years, and I don't think you can get a new replacement..Iboats has the conversion kit: http://www.iboats.com/mall/partfinde...n_id=241431610

Since the UFI has the sensor coil built in, it can have nice spark, but out of time. I've seen it once, and found a used replacement from Tim's outboard at a nice price: 218-682-2331, and problem solved.

If you have a timing light, you can verify that the timing is indeed out of spec before replacing..

Good luck!

 

[btkees]

So when graciously acquired the engine, I rebuilt all the rebuildables since it sat for YEARS. After burning through sparks plugs and seeking all your generous input. You all pointed me a step, hopefully to the successful end of troubleshooting.With the lack of attention to detail and further knowledge of the outboard specs, I was swapping out the wrong type of plugs with what was installed when I received the outboard. A standard small engine plug. I finally got the recommended alternative L77JC4, since they didn't carry the Q type. What is the difference between the two?
Hopefully this is the cure all and I didn't do any further damage when I got try it out.
Thanks for taking the time to help out a rookie.

 

[Chinewalker]

The QL77JC4 are a suppressed plug. You are fine with the L77JC4. I actually prefer them, myself, but then I don't run any electronics in my boats, either, so no suppression needed...

 

[David Young]

And local auto parts stores carry these spark plugs, and even Walmart