Spark plug burn - check it out

1968 -1970 Mopars

  1. pearljam724

    pearljam724 Well-Known Member

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    My engine had been running a tad lean. I rejetted it to my liking and I’m shooting for a very light tan plug reading. The plugs were previously fairly white and it’s now tuned to my liking. I didn’t pull other plugs, but #1 cylinder I did. There’s absolutely nothing wrong with my engine and it’s running a lot better now. But, this plug reading is weird. I tried to take the best pic of it I could. If you look closely the plug burn is split perfectly down the middle like someone cut it with a laser. Left side is where it use to read prior to jet increase and right side is the reading I was shooting for. I’ve seen this once or twice over my life. But, have no idea why a burn splits perfectly down the middle like this ? No big deal, just curious as to why ? Autolite 65, soon I’m going to switch to a slightly colder plug, Autolite 64.

    B2FEC6BA-A96D-4F51-9369-BF731FC56366.jpeg
     
    Last edited: Nov 6, 2019
  2. moparnation74

    moparnation74 FBBO Gold Member FBBO Gold Member

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    Normal
     
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    • pearljam724

      pearljam724 Well-Known Member

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      I would think so too. Just strange that it would burn this way. Probably, put a little over 30 miles on it since I recalibrated the carb.
       
    • Bee1971

      Bee1971 Well-Known Member

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      His Fingers , Sure

      LOL

      All I see is a blurry spark plug
       
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      • pearljam724

        pearljam724 Well-Known Member

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        Agree, $700 phone. Not happy, lol !
        Zoom in, man. Lol !
         
      • moparnation74

        moparnation74 FBBO Gold Member FBBO Gold Member

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        As simple as that....Heck even a "cave man": can do that:lol:
         
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        • beanhead

          beanhead FBBO Gold Member FBBO Gold Member

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          Blurry any way you look at it. You're only seeing idle mix at the top end of the porcelain btw. How do you know you need to go colder? 2-3 threads max should show heat discoloration if heat range is good. Tough to see on the autolites with the black threads but impossible from that picture.
          To get a true reading you need to cut the threads completely off.
          20191106_164433.jpg
          (This was rich at WOT but I hadn't got to that stage of tuning yet)
           
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          • moparnation74

            moparnation74 FBBO Gold Member FBBO Gold Member

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            Impossible for you beanhead.....

            No one said the picture wasn't blurry.....I see enough....:D
             
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            • pearljam724

              pearljam724 Well-Known Member

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              Thank you. But, for me I don’t think that was necessary. I could see down inside the plug and it was the same uniform all the way down inside when it was running too lean. Pretty much the same exact reading as picture you posted. I understand that reading was an idle reading. But, I also read plugs at mid and high throttle. I just was wondering if anyone knew a logical explanation for that wasn’t the first time I’ve seen it. I would think the burn should be uniform all around. There is a reason why, I’m just being honest and saying I don’t understand why. I know it was lean at wot based on lack of power pulling very long and very steep hills. It pulls same hills a lot better now. Night and day. I had the hottest plug in it. Want to see how it runs dropping down a step, that’s all. Time for new plugs anyhow.
               
            • beanhead

              beanhead FBBO Gold Member FBBO Gold Member

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              Mine always show color only part of the way around at the top too...cruise/mid/wot wraps around, but not what's on the exposed area. I always wondered if it had something to do with the ground strap being right there? Or maybe it's today's awesome fuel lol..
               
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              • pearljam724

                pearljam724 Well-Known Member

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                You might have it there. Could be the way this cheap fuel is burning. Something is causing it to not to burn all the way around the plug. Maybe, weak spark. I have new quality wires, cap, rotor, new supposedly quality coil, etc. I have a tool to check spark strength. Maybe, I ll check that. Just wondering if there was a reasonable explanation, that’s all. No biggie
                 
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                • 1 Wild R/T

                  1 Wild R/T Well-Known Member

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                  Now I'm disappointed.. I saw the title & thought you had burned yourself changing plugs.... Lord know I burned myself a few times changing plugs....

                  I was looking forward to seeing someone else enduring pain due o these old cars...:lol:
                   
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                  • pearljam724

                    pearljam724 Well-Known Member

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                    That’s how you real’em in, deception. Lol ! You’re not alone. Can’t count how many times I burned myself on my aluminum radiator, reaching for something.
                     
                    Last edited: Nov 6, 2019
                  • 493 Mike

                    493 Mike FBBO Gold Member FBBO Gold Member

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                    Was it just one plug? I'm leaning toward flame front and plug orientation in the chamber.
                    Mike
                     
                  • pearljam724

                    pearljam724 Well-Known Member

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                    Only checked one plug. I always bottom plugs out with about 10 pds of torque. Maybe, forged pistons could cause it depending which way plug is turned. I’m not even sure I have forged pistons though. Because heads have never been off by me and it does have an unknown larger cam. Maybe, higher valve lifts. Maybe valve seats need redone. It has matching numbers original 360 cast heads. I never did a compression test. Could be one of several reasons. No clue. Sounds very healthy, runs very good, good power
                     
                    Last edited: Nov 6, 2019
                  • moparedtn

                    moparedtn FBBO Gold Member FBBO Gold Member

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                    You wouldn't have to swing a dead cat very far around here to hit a fellow sufferer... :)
                     
                  • RJRENTON

                    RJRENTON FBBO Gold Member FBBO Gold Member

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                    IMO....
                    The reason for the definitive coloration MAY be due to the shrouding of the plug as its installed. Remember, spark plug's insulator is cooled by the incoming fuel charge (tan colored portion) and the white color portion is exposed to the combustion chamber flame side which may result in the lighter color.
                    Spark plug electrode design and composition greatly affects its operation and how it colors. I was told years ago, the "best" way to determine plug heat range and mixture distribution was at the end of a 1/4 mile contest at full throttle and load was to kill the ignition, declutch or shift to neutral, and coast to a stop, WITHOUT decelerating in gear. This would provide the best determination of the combustion process. Is this the correct way??? Its up to you to decide... The original pix appears to be from a good "healthy" engine...
                    BOB RENTON
                     
                  • Cranky

                    Cranky Moderator Staff Member FBBO Gold Member

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                    You could throw in a new plug and see if it turns out the same.....and 700 bucks for a phone?! Mine takes pretty decent pics for 175. My old phone was horrible. If you didn't hold it steady Eddy, it was total blur. It needed a tripod but it was free.
                     
                  • pearljam724

                    pearljam724 Well-Known Member

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                    You’re right, Bob. That’s how you read jetting - plug reading for high rpms. Otherwise, when idle drops. Plug will read a idle burn. During wide open throttle, turn key off and let car coast to a stop, check plug. As you stated.
                    Same technique for mid throttle. Car has to be moving. You can also determine high rpm jetting by pulling power up a long steep mountain incline because engine is a under constant load at high rpms. Rather than flat ground.
                     
                  • pearljam724

                    pearljam724 Well-Known Member

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                    I agree. My last model phone (IPhone 6) took better pictures and this model (IPhone 7) supposedly had a better camera. Nice pics outside. But, not inside. Poor zoom quality. I was happier with the previous one.
                     
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