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Spark plug reading on my 998cc mini.

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  • Spark plug reading on my 998cc mini.

    curious about my plugs... ignore the threads as that is just lube... and a dab of that smeared on the edge (left lip area) of the top too. but the color may be slightly right no?

    This is on my green mini.... These were pulled after approximately 7500miles - which has had some dieseling or run on issues... so recently i pulled these plugs "BP6ES" gapped at .023 and replaced them with BP7ES gapped at .026 - and don't notice any difference of performance really, it seems to run-on/diesel much less... And NO, i don't just let it diesel when i shut off the car, i am told the best thing to do is rev the car up real good to around 3k or so and turn key off quickly and then press the gas pedal to the floor to open the throttle to allow all air to come in and flush out fuel... works 100% of the time to shut off engine clean and no diesel or run on. (although i get looks from people around me thinking i'm trying to show off the sound of my exhaust, better that then them hearing my mini run-on and knock)

    I'm thinking maybe the colder plugs might reduce dieseling run on...

    Also i'm curious if my HIF38 should be adjusted just a hair to get a slightly leaner mixture.

    My engine is a Pre-A block cooper 998, TAM2052 flat top pistons, mild cam of some sort, 12g295 head, Pertronix Ignitor elec ignition, Lucas Sports Coil, HIF38 carb, AAM needle, ITG sock filter and billet stub stack (sold at 7ent) . If i remember correctly the cars compression ratio is around 10.5:1 from what i was told. Car seems to run good, but wonder what others may suggest. I used to run a HIF44 and quickly pulled that and put in an HIF38 with an AAU or AAA (about 200+ miles) (cant remember, and can't seem to find the needle in my spares) Anyways, it ran better then the HIF44, but overall poor with the other needle until i decided to try the AAM needle... a major improvement in torque and overall power...ran it this way for about 7000+ miles. I thought the spark plugs should be slightly lighter brown then the photo above? (note:these plugs havent been changed for around 4-5 years)

    i found this interesting article:

    and also this

    Is there a local shop that can accurately tune an SU carb for the rull range of RPMS and keep the A/F ratio correct along the full range. Anybody that actually specialize in this?

    Comparing them to my SPI mini, well the SPI mini plugs are damn near perfect looking comparing it to the charts. Would like to get the optimum performance out of my Carb Mini too..
    Last edited by ; 05-19-2009, 07:08 AM. Reason: added info

  • #2
    Retarded timing on my 998 contributed to run-on. Don


    • #3
      Looks like a Purrrfect Rust Beer Brown!!

      Seriously, it is sort of hard to give an accurate reading to plugs that have seen their better days. I know you know that so please don't be insulted.

      It looks like they may have been out more than once as there is a slight bit of thread exposure to the combustion chamber, which would more than likely happen after multiple squashings of the spacer washer.

      I've always been of the opinion that one obtains the readings after the plugs have been in operation a couple hundred miles. That way there is a clean white palette for the ignition to colour.

      Oh and it looks like the threads are well lubricated, it must have come from an English car!!

      Cool website too! At least your plug has a ground strap and is not melted! I like the carnage pictures too.


      • #4
        To add to this... i was talking with chuck last night about this...and two things i forgot...but it appears the car is slightly running rich.... so i want to back off the richness a tad.... the screw i found...forgot which way to turn it though...

        second question... what is the proper way to get an accurate reading on "how rich" or "how lean" it should be with the technique that chuck explained to me, yet of course i forgot today. I removed the air filter and feel the dashpot thingie and can sort of pull it upwards... thats about as much as i remember... something to do with the engine revs going up and down, yea yea... Anyways, anyone can fill in the blanks an let me know how to do this correctly?



        • #5
          There was a third issue. Because you are running an additive (cause of the odd color of the plugs) it makes it harder to read them. They do appear slightly rich, but it's hard to tell from the photo and odd color.

          HIF adjustment screw turns clockwise to richen.

          Lifting the piston slowly will give you a good indication of the air/fuel mixture around idle. It's not going to help much at higher rpms if the car setup and needle being used are other than standard. "Plug cuts" are a better way, and getting the car on Doug's dyno would be the best.

          Lift the piston slowly. If the engine stumbles and wants to die: too lean. If the engine speeds up as the piston is raised and continues to do so for a while: too rich. If the engine initially speeds up and then slows down: just right.
          Last edited by Cheleker; 05-21-2009, 06:07 PM.
          The more I know about Minis, the more I know I don't know about Minis.


          • #6
            Definitely found a sweet spot backing it off a hair... top end is a bit better, and idles a tad smoother too. overall torque is slightly better... Not a massive improvement, but noticeable.


            • #7
              I've changed from an AAM to an ADX needle and improvement performance noticeably. But still have run on. I will be installing a new HIF38 carb soon, and will try messing around with the idle speed as i'm pretty sure that has to be the problem. its a tad high i think.

              But the plugs read a better color now then before.

              WinSU works pretty darn good in getting an accurate needle choice.
              Last edited by ; 09-20-2009, 09:18 PM.