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  •  » Spark plug condition??

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    9/11/2022 11:16 AM  #1

    Rudi
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    From: Stuck in the 50's Welland Ca
    Registered: 4/01/2013
    Posts: 3,973

    Spark plug condition??

    I pulled the plugs from my 331 and saw that the they are all over the map on how they read.
     The engine idles and runs  very good other than an occaisional stumble at idle.
     most of mt driving these fdays rarely sees the rpm go higher tha 25-3000, I drive like and old man, which I am but do have a teen age moment once in a while.
     Any inputs on why the pluge read so far apart. They are in the holder as is the firing order.






     

    Good work ain't cheap, Cheap work ain't good!   Simple Man
     

    9/11/2022 11:36 AM  #2

    6sally6
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    From: Surfside Beach,SC
    Registered: 4/02/2013
    Posts: 6,850

    Re: Spark plug condition??

    With crappy gas ....periods of idle...slow driving habits...etc.
    ya can't 'really' try and deduct anything from "readin-the-plugs"

    New plugs............wide open rip through-the-gears.....cut engine......THEN read the plugs. (then its still a guess if ya axe me!)

    My advice.......while they're out...wire brush and clean 'em
                                                        re-gap 'em (maybe...adjust the gap?!)
                                                        try a new set of wires
                                                         re-check timing
                                                        re-adjust carb(maybe with a vacuum gauge)
                                                        let that 'spirited teenager mentality' out more often!! (you remember..."blow-it-out" more)
    6sally6

    Get busy Liv'in or get busy Die'n....Host of the 2020 Bash at the Beach/The only Bash that got cancelled  )8
     

    9/11/2022 1:59 PM  #3

    Bullet Bob
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    From: Montrose, Colorado
    Registered: 4/01/2013
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    Re: Spark plug condition??

    Did you have the same intake on the old engine, Rudi?  Did it run even on all plugs?  Just wondering, that looks like it might correspond to runner length, doubt it but.....  Do you  have an AFR gauge?  If so, what's it running at going down the highway?
    And what Sal says is true.  The only way to get a valid read on plugs is to do a WOT run and a clean shut-down.  Or a long run at speed.
    Also, #3 looks like it might be oiling just a tad.

    Last edited by Bullet Bob (9/11/2022 2:00 PM)

    "you get what you pay for, good work isn't cheap, and there are NO free lunches...PERIOD!"
     

    9/11/2022 3:11 PM  #4

    BobE
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    From: White Plains, NY
    Registered: 4/04/2013
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    Re: Spark plug condition??

    Is the manifold a 4-hole or open chamber directly where the carburetor mounts?  If it is the 4-hole type and you’re not opening the secondaries much, there could be an atomizing issue within the manifold.  This maybe a long shot, but something to check. 
    Correlate the plugs to the dual plane manifold ports, and see if those ports are supplied mostly by the primary or secondary side of the carburetor. 
    Also, check the spark plug wires, distributor cap and rotor, you may not be getting full spark to some cylinders. 
    PS – I like your very official looking spark plug stand and labels.  I usually use a piece of cardboard and punch holes in it to hold my plugs for inspection.

    65 Fastback, 351W, 5-speed, 4 wheel discs, 9" rear,  R&C Front End.
     

    9/11/2022 3:42 PM  #5

    Rudi
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    From: Stuck in the 50's Welland Ca
    Registered: 4/01/2013
    Posts: 3,973

    Re: Spark plug condition??

    Bullet Bob wrote:

    Did you have the same intake on the old engine, Rudi?  Did it run even on all plugs?  Just wondering, that looks like it might correspond to runner length, doubt it but.....  Do you  have an AFR gauge?  If so, what's it running at going down the highway?
    And what Sal says is true.  The only way to get a valid read on plugs is to do a WOT run and a clean shut-down.  Or a long run at speed.
    Also, #3 looks like it might be oiling just a tad.

     
    IIRC the plugs were about the same on the 289Plug wires are good.
    I’m not trying to get a plug reading for Wot, just showing the difference in the plugs condition after a long casual drive.
    Using 91 octane Costco fuel.
    The intake manifold is an Edelbrock performer RPM, open chamber.
    I’m not concerned about the mains  jetting at WOT the AFR shows just a tad rich.
    At idle the AFR says rich but the idle is very good with the exception of an occasional stumble, 750 in gear, 850-900 in neutral.
    The cam is not radical.
    I’ll have to dig out the go-pro and see if I can remember how to post a video.
    I put new plugs in today and see if they change anything.
    If not I’ll move on to replacing the cap and rotor and the to check float levels and put a vacuum gauge on it.

    Last edited by Rudi (9/11/2022 3:51 PM)

    Good work ain't cheap, Cheap work ain't good!   Simple Man
       •Thread Starter
     

    9/11/2022 4:53 PM  #6

    Bullet Bob
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    From: Montrose, Colorado
    Registered: 4/01/2013
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    Re: Spark plug condition??

    You say it's running rich at speed and at idle.  How rich?  I'm leaning toward an anonymization issue that's causing some runners to be lean and some to be rich.  Rich is never a good idea as it causes excess cylinder wear, wastes that cheap fuel, and stinks.   As for it idling nice, there is no reason why a properly tuned carb can't idle just as well.  Just sayin'.

    "you get what you pay for, good work isn't cheap, and there are NO free lunches...PERIOD!"
     

    9/12/2022 3:34 PM  #7

    MS
    Forum Originator

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    From: Canyon Lake, Texas
    Registered: 1/24/2013
    Posts: 12,246

    Re: Spark plug condition??

    Seems like that pattern might follow the runners on the intake, with one side of the carb feeding two outer on one bank and two inner on other bank. If that is the case, there could be obstruction or fuel leakage on the side with corresponding lean or rich plugs.
    Maybe setting jets on the rich side one size lower?

    Just a thought.  I know the experts sometimes fine tune a carb in that manner, but I am certainly not one of them.

    Money you enjoy wasting is NOT wasted money... unless your wife finds out.
     

    9/12/2022 3:45 PM  #8

    BobE
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    From: White Plains, NY
    Registered: 4/04/2013
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    Re: Spark plug condition??

    Rudi - just a reminder, if you have one AFR gauge, which is usual, it is reading the AFR of a combination of cylinders.  As such, some cylinders could be lean, others rich.  To truly see what each cylinder is doing you'll need an oxygen sensor on each cylinder.

    65 Fastback, 351W, 5-speed, 4 wheel discs, 9" rear,  R&C Front End.
     

    9/12/2022 11:15 PM  #9

    Nos681
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    From: Atlantic Mine, Michigan
    Registered: 7/14/2016
    Posts: 3,329

    Re: Spark plug condition??

    Looks like you have a dual plane intake manifold according to the plugs.

    Perhaps the the “rich side” could be leaned out a little bit.

    I would also check the resistance of your plug wires and see if all are similar.

     

     

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