74-76 15hp Spark Plug Recommendations

[JohnnyGuy]

Hey all,

Having done lots of reading on the subject it seems that there is differing opinions on the subject based on the way the motor is used and regional environmental (temperature, altitude, etc...) conditions.

Leeroy's page makes note of using Champion plugs and NGK (B6HS, BR6HS and B7HS) plugs. It also makes reference to gapping them at 0.04 (1mm) to reduce fouling.
NGK page makes reference to using BZHS-10 (inductive resistor) plugs.
I cannot find my specific motor on the Champion website parts lookup, however OMC recommends Champion UL81J.

I live in Ontario Canada. Primary use of the motors is for fishing, so there is quite a bit of trolling involved, some WOT runs to and from fishing locations, etc...

Having done some reading last fall after purchasing the motor (came with the boat), I purchased B6HS plugs and gapped them to 0.40 (1mm) in hopes that the hotter plugs and larger gap would have a tendency to reduce fouling of the plugs due to the trolling runs that this motor will partake in. This was based on Leeroy's site that mentions an outfitter using the B6HS plug in his fleet on a colder high altitude lake and having good experience with less fouling.

I wanted to know what some others with the same motor have run and what your experiences have been.

From my reading, with the Points and Condenser on these motors I'd have no problem running a resistor (R) plug, but I'm wondering if I really need to do so.

The plugs I pulled off the motor last fall (installed by the previous owner) were BR6HS and were fouled (I was having an issue with only running on one cylinder at the time).

I then installed B7HS and ran them for the rest of my trip. I then ran a SeaFoam treatment through the motor and fogged the motor with them in before storing the motor for the winter last fall.

I recently rebuilt the carb, fixed the starter recoil and installed the new plugs (B6HS-gapped at 0.04) as mentioned above.

I now find myself needing to purchase a spare set of plugs to have on hand and I cannot decide with what to go with.

I'm interested to hear what others have to say.

FWIW, my specific motor is '76 Johnson (15R76A)

Thanks in advance,
JohnnyGuy

 

[racerone]

First thing is to check operation of thermostat.----They often fail stuck open and motor will run cold.-----Lots of other wee issues with those early 9.9 motors too.----Where in Ontario, I have heard it is fairly big like 30 hrs to drive from one end to the other.

 

[Sea Rider]

Better write the OMC Company and ask which plug type that OB uses so not to wild guess or go for someone else recommendaions. A NGK 6 plug is hotter than a 7 by around 100°. Can use plugs with resistor (R) or not, just gap the electectrode tigh with a feeler gauge to specs. On 2 strokes OB's the plug fouling will be same if the OB is run for extended time periods when throlling no matter which standard type pulg you use or at which gap they were adjusted to. It's the nature of the 2 strokes beast.

This accounts for the plug not reaching its self cleaning tip temp which is achieved at over + 500 C°, under it will foul plugs hopelessly. If plan throttling extensively would recommend going back to terra firme from your fishing spot at full throttle as if you were stealling the combo for plugs to be cleaned on its way back. On next boating occasion OB will cold start faster.

Yep, install a new thermo along thermo gasket, those are Jurassic ones...

Happy Boating

 

[JohnnyGuy]

Where in Ontario, I have heard it is fairly big like 30 hrs to drive from one end to the other.

Most of the time the boat will be run in lakes around the Muskoka and Haliburton areas.

 

[JohnnyGuy]

If plan throttling extensively would recommend going back to terra firme from your fishing spot at full throttle as if you were stealling the combo for plugs to be cleaned on its way back. On next boating occasion OB will cold start faster.

The ol' "Italian Tune-up"; that what I had planned on practicing!

Thanks for the other advice thus far gentlemen!

 

[racerone]

One thing to do is change the thermostat.----Easy to do when powerhead is of for possible plugged idle relief holes.----Seen that on problem motors like that.

 

[F_R]

UL-81J (now UL-81C) is a booster gap spark plug, not a resistor plug. There is an air gap within the plug that the spark must jump on it's way to the gap at the tip. That extra gap forces the spark voltage to increase, helping it to fire through fouling.

 

[JohnnyGuy]

One thing to do is change the thermostat.----Easy to do when powerhead is of for possible plugged idle relief holes.----Seen that on problem motors like that.

Plugged idle relief holes?

 

[racerone]

Yes , some will argue.----I have seen the holes at the top of the exhaust tuner plugged solid with carbon.----Can not be seen without taking powerhead off.----And I have some of those motors and have taken more than one apart too.

 

[Sea Rider]

If the exhaust tuner is same as the exhaust pipe with different name, Racerone is quite right. Have seen the exhaust pipe, pistons and exhaust chamber of a 18 HP severely blocked due to using OB with too much oil added to fuel while extensive trolling was done on short runs for months, add bad quality 2 strokes oil too.

Wrote Brisk and inquired about air plugs, said that will foul much less than standard plugs but inevitably will foul if too much trolling is done at very reduced speeds for extremely long time periods. Those plug are excellent for constant higher speeds runs and quite expensive too..

Happy Boating

 

[JohnnyGuy]

I perhaps should also make clear that currently I am not having issues with constant plug fouling.
I am simply trying to avoid fouling as best as possible (extended plug life).
With that being said, the above information regarding thermostat replacement, plugged relief holes will be kept in mind should I start to experience frequent fouling OR I pull the powerhead for any reason.

 

[racerone]

That motor may not be the best option for lots of trolling.

 

[JohnnyGuy]

That motor may not be the best option for lots of trolling.

I've had this mentioned to me previously, it's the motor that came with the boat and not all of my fishing is exclusively trolling.
Cheers!

 

[Faztbullet]

It will help if you set the engine level instead of tilted under.

 

[JohnnyGuy]

UL-81J (now UL-81C) is a booster gap spark plug, not a resistor plug. There is an air gap within the plug that the spark must jump on it's way to the gap at the tip. That extra gap forces the spark voltage to increase, helping it to fire through fouling.

Purchased the UL81C plugs as my current backups.
I was able to find the motor on the champion website and these are one of the recommended plugs for the motor.

Thanks for all the recommendations and pointers from all who replied.

Cheers.