spark plugs

[Clem]

Hello all....here is my question. my boat motor uses spark plug L77 JC4 and i have been told that i need to use a hotter plug. i need to know what using a hotter plug does. what is the advantage. and what would the number on the plug be? thanks in advance

[rolmops]

If you are running a Johnson/Evinrude in the 35 to 50 horse range (not commercial)and you run a lot at sustained high speed you want to try a 78 instead of a 77.

[Clem]

its a 90 hp 2 stroke

[BullGator]

Hotter plugs are often used in engines that have an excessive amount of blow-by, caused by cylinder wear or piston/ring wear, and valve wear in 4-stroke engines. The result is lower compression, which in turn lowers the "volatility" of the ignition explosion. Over time, the spark plugs will become loaded up with mineral deposits that were left behind due to the incomplete combustion.

So, higher temperature plugs (usually one number higher) are used to counter the effects of incomplete combustion.

However, it should be said that many a "hotter" plug has been installed due to an incorrectly tuned carburetor.......not cylinder wear. But that's another story........

Improper ignition timing can also cause these symptoms.

If he has not done so, have your mechanic perform a compression check, and a leak-down test. This will show whether the issue lies in the cylinder(s) or its a carb problem.

I often install a hotter plug in motors that troll alot, but you have to know how to "read" the color of a used plug and check them often.

[tree top flyer]

Now Im no expert but I believe that people who troll a lot will run a number hotter to try to avoid build up in there engines from low rpm for hrs and hrs. Done this and it seemed to work~ but again a good carb or Valve adjustment prob do the trick also

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[Wrestling Coach]

I changed years ago to NGK B7HS-10. I have a Johnson 90HP 2 stroke. I troll a lot on Erie for hours at a time. I run synthetic 2 stroke oil injected. Engine never skips a beat and never fouls these plugs.

Dennis

[c.bonaffine]

Irun a 90hp johnson,the champion plugs seemed to foul out quicker. 10 years ago i switched to AC Delco plugs M40FFX.This ac plug is a direct cross with theCHAMPION. Motor ran much better one set of Ac's per season. My buddy has a 75h.p. Evinrude same problem w/Champion,swiched to the Ac plugs 100%better .Both are two strokes.The 90 h.p. had acomplete rebuild 12 years ago.

[Fish Hunter]

If a "hotter" plug is being recommended, to put a band-aid on a problem, I'd fix the problem.

[Knotlost]

It depends on why the "hotter plug" is being recommended.

If your having trouble loading up because of long hrs of trolling, then its very reasonable.

But I got some advice that has been great. I was told by a couple of guys that work on boats for a living, and they build the big water cigarette boats, and have done very well at racing them as well, to get the bosh 2 if I'm remembering it right. They are the bosh plug at wall mart that have the two electrodes over the post in the plug. They do make a "3" but they are not needed. They make them generically so you pick the one that is the right length and thread size. I have since used them and they are great, no loading ever, and they are not "hot" like going to a hotter normal plug, they just don't ever load up and fire reliable.

[Mortigan]

Looks like those are the Bosch Platinum+2 spark plugs.

[Knotlost]

Thats the name I couldn't remember the exact name but that it.

[L&M]

If a "hotter" plug is being recommended, to put a band-aid on a problem, I'd fix the problem.

Very good advice to heed with a 2-stroke engine. ( especially with an older V-4 omc ) Granted different brands seem to be better when it comes to fouling. BUT always stay with in the recommended manufacturers heat range & recommendations. He's not talking a 4 stroke I/O or inboard engine here. Pistons are by far more expensive than correcting the issue that is causing it.

[irishbailey86]

i troll with old 2 stokes...a six horse johson and a 9.5 evinrude....i run them one up from j6 to j8's for trolling works great....i can slow down to a slow putter and u can barely tell theyr running.

[Misty IV]

i troll with old 2 stokes...a six horse johson and a 9.5 evinrude....i run them one up from j6 to j8's for trolling works great....i can slow down to a slow putter and u can barely tell theyr running.

Ditto!!! My kicker is a 1971 Johnson 6hp 2-stroke and it runs like a dream. Has never let me down.

[Shakemsam]

Closing up the gap a bit, can help if you troll a lot as well. Stay away from any of the "Split Fire"

type plugs unless you want a hole in your piston!

[Fish Hunter]

When closing the gap, it will decrease the size of the spark kernel, but it will enhance the intensity.