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Otto Throttle View Drop Down
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    Posted: March-01-2025 at 10:41am
Ok I don't mean to "Spark" any controversy but here goes....

Spark Plugs...Mine HO, 285 HP,  Carbureted (GT40 Heads)  calls for the WL764s.  I have seed both the standard, copper, and platinum electrode versions....I am still running the factory original plugs, but I want a spare set...just in case.  What brand and electrode are you running out there!


Thanks in advance!

Otto
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TRBenj View Drop Down
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Points: 21197 		Post Options Post Options   Thanks (0) Thanks(0)   Quote TRBenj Quote  Post ReplyReply Direct Link To This Post Posted: March-01-2025 at 3:23pm
Standard is copper and the best conductor- should offer the best performance and lowest price. The advantage of the platinum and iridium tips are longevity, you’re usually best served running the copper and replacing them more often.
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Otto Throttle View Drop Down
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Thank you!!!
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Jonny Quest View Drop Down
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Some have indicated that the Autolite 764 is discontinued.  They can still be found, especially on the internet.

The Autolite 104 is the replacement plug for the 764 and is basically the same plug -- 104 has full threads on the body and the 764 is threaded halfway.  Either will work.  (GT-40 or GT-40P heads)

JQ
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KENO View Drop Down
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One thing to keep in mind here is that 

A copper plug typically has a nickel center electrode with a small diameter copper wire buried  in the middle of the center electrode

A platinum plug has that same small diameter copper wire buried in the middle of the platinum tipped center electrode

An iridium plug has that same small diameter copper wire buried in the middle of the iridium tipped center electrode

You can't visually look at any spark plug and see any copper. (unless you destroy the plug to get at look at it)

And like mentioned earlier, the copper core standard plug will be just fine in your engine Otto

And Otto..... you should probably change those plugs a little more often than every 27 years or so.  Wink
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Otto Throttle View Drop Down
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What is the difference between full threads or half threads? Does one run cooler than another?

Yea I know… my cousin has the same boat except an 1998, and he has never changed plugs either! He has 400 hours on his and I have 500 on mine. I was thinking when changing them to soak the threads with kroloil for a few days…..

That being said we are checking driveshaft alignment and repacking the rudder and drive shafts this spring! Any tips on those projects?
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Otto Throttle View Drop Down
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Also what do the prefix’s mean before the number…. WL or AR… what if there are no prefixes?   
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Jonny Quest View Drop Down
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Full Threads vs. Half Threads

The thread length shouldn't affect anything. I believe that you are thinking about the plug's heat rating.  Per the Autolite catalog, both the 764 and 104 plugs have a heat rating of  9.

I ran both the 764 and 104 in my 1994 and 2001 boats -- both with the High Performance Ford 351W.  Just for giggles, I change spark plugs every couple of years.  My OCD lizard brain...
Anyway, I would pull the plugs and they both looked and performed the same.

JQ
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2003 Ski Nautique 206 Limited

Previous
2001 Ski Nautique Open Bow
1994 Ski Nautique Open Bow

Aqua skiing, ergo sum
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Jonny Quest View Drop Down
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Autolite Copper

Spark Plug - 
764
Specifications:
Center Electrode DesignStandard
Center Electrode Tip MaterialNickel
Ground Electrode Tip DesignStandard
Ground Electrode Tip MaterialNickel
Hex Size (Inch)5/8
Thread Diameter (Millimeter)14
Reach (Millimeter)17.2466
Seat TypeTapered
Pre-Gap Size (Millimeter)1.1176
Manufacturer Heat Range9
Center Electrode ProjectionMid Projection
Spark Plug - 
104
Specifications:
Center Electrode DesignStandard
Center Electrode Tip MaterialNickel
Ground Electrode Tip DesignStandard
Ground Electrode Tip MaterialNickel
Hex Size (Inch)5/8
Thread Diameter (Millimeter)14
Reach (Millimeter)17.2466
Seat TypeTapered
Pre-Gap Size (Millimeter)1.27
Manufacturer Heat Range9
Center Electrode ProjectionMid Projection
Current
2003 Ski Nautique 206 Limited

Previous
2001 Ski Nautique Open Bow
1994 Ski Nautique Open Bow

Aqua skiing, ergo sum
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Jonny Quest View Drop Down
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Points: 3009 		Post Options Post Options   Thanks (0) Thanks(0)   Quote Jonny Quest Quote  Post ReplyReply Direct Link To This Post Posted: Today at 10:30am
Autolite spark plug prefix list:

XP = Iridium
AI = Ultra Iridium
AP = Platinum
APP = Double Platinum 

JQ
Current
2003 Ski Nautique 206 Limited

Previous
2001 Ski Nautique Open Bow
1994 Ski Nautique Open Bow

Aqua skiing, ergo sum
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