Ignition upgrade advice

Electrical & Ignition

  1. Charlied

    Charlied Well-Known Member

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    Have 74 big block with completely stock mopar ignition set up, runs fine,but has a tendency to foul plugs. Carb leaned out, timing set right, wires good, rotor and cap good.

    Just wondering if spark is weak or on the edge. Wondering if putting in a MDS box or something similar would help to deliver more bang ? Engine was professionally rebuilt a while ago ,rebored 30 over, all new internals. Think maybe the crap gas today (ethanol) doesn’t help either. Any suggestions, without going nuts.
    Thanks
     
  2. steve340

    steve340 Well-Known Member

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    You could try another coil - is the spark plug heat range correct? Plug fouling can be a few things.
     
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    • Charlied

      Charlied Well-Known Member

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      Plugs are champion RJ12YC which are correct for the 400 4bbl.
      Read that prolonged idling could also be the culprit. A different coil is an easy thing ,will try it.
      Thanks
      Charlie
       
    • RJRENTON

      RJRENTON FBBO Gold Member FBBO Gold Member

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      Regarding spark plug heat range. If you're satisfied with the engine settings (ignition advance curve + mixture settings), prolonged idling, can definitely cause "cold fouling" even though the plug's heat range is correct for all other aspects. Perhaps consider a different brand of plug and construction of the same heat range of the Champion RJ - 12Y C. Autolite AP-85 or AC R-43S or R-44S or NGKs work well. Personally, I use either Champion UJ-11G or or HO-8A, which are non projected nose, platinum electrode types and resist cold fouling because of their small center electrodes, in my RS23V0A******, which has 11.0:1 TRW pistons, Crane cam, 4.10 gears, etc. Plugs are relatively inexpensive....try some alternative types and configurations. Just my opinion of course.
      BOB RENTON
       
    • Charlied

      Charlied Well-Known Member

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      Thanks Bob for the advice and suggestions. Will check my coil first to be sure it’s working properly then try an alternative plug. Car is a cruiser so looking for smooth idle and performance.
       
    • 747mopar

      747mopar FBBO Gold Member FBBO Gold Member

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      This is just my take on MSD or other aftermarket high perf ignitions, they're a waste of money for stock-mild builds. They have their place so don't get me wrong but sometimes simple is better. I'd do as recommended by RJ and sort it out, when your done you won't be at the mercy of non off the shelf parts.
       
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      • Don Frelier

        Don Frelier FBBO Gold Member FBBO Gold Member

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        You can take a spare plug and use a jumper cable to ground. Crank it over and view the spark it should be blue/white and crisp.
        Try it at night if your eyes are bad like mine.
        If it's yellow and lazy you've got a problem.
        I'd consider advancing the timing even just as a test try adding 5 and then 10 more degrees initial advance.
        If that improves your starting and low speed response then you likely need to limit the mechanical advance to get the correct overall max advance.
         
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        • threewood

          threewood FBBO Gold Member FBBO Gold Member

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          Agree with trying a hotter plug first.
           
        • Charlied

          Charlied Well-Known Member

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          Agree with your suggestion also known as the KISS method (Keep it simple stupid) I’m guilty of over complicating this.
          Given the champion RJ12YC as the base line what is the next step up hotter plug. Sorry to show my ignorance. This plug has probably about 50 miles on it and what I’m dealing with. Thanks for listening. 6F37F633-21B1-42E6-991A-08B83E47DE22.jpeg
           
        • Charlied

          Charlied Well-Known Member

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          Sage advice as car is bone stock.Thanks again
           
        • 451Mopar

          451Mopar Well-Known Member

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          Looks like carb is too rich. Work on tuning the carb first. First part of that is checking fuel level in the fuel bowl(s)
           
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          • Don Frelier

            Don Frelier FBBO Gold Member FBBO Gold Member

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            Is it a ThermoQuad? Some of those had a problem with floats sinking with age they weren't a soldered brass float (I think)
             
          • RJRENTON

            RJRENTON FBBO Gold Member FBBO Gold Member

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            If you were considering Champion, I would suggest J-13Y or Mopar P35P (made by Champion available on line) or AC R44S or Autolite AP86. Usually, plugs with platinum electrode(s) and most copper alloy center electrodes (Champion - C designation), have a wider heat range. NGK plugs offer many different styles and types of electrode configurations and heat ranges. Just be careful when selecting plugs as the "reach" or thread length is an extremely important consideration. MOPAR iron heads use 3/8" reach plugs; some aluminum heads use 3/4" reach plugs.
            BOB RENTON
             
          • Charlied

            Charlied Well-Known Member

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            Appreciate the advice, will double check carb setting ( lean it out more) and try the hotter champion plug. Where on line are Mopar plugs?
            Thanks
            Charlie
             
          • Charlied

            Charlied Well-Known Member

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            Yes thermoquad. I very carefully rebuilt it short time ago and replaced the brass floats with phenolic ones as part of the rebuild.
            Thanks
            Charlie
             
          • Charlied

            Charlied Well-Known Member

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            BTW checked the coil with my ohm meter, it’s fine and in specs. So can eliminate that as the problem.
            Thanks
             
          • RJRENTON

            RJRENTON FBBO Gold Member FBBO Gold Member

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            Try ebay (vintage Mopar spark plugs) or Google Mopar P34P or P35P spark plugs or Champion J13Y or J14Y. Or if considering a non projected core nose plug, try Champion J-8 or AC 44 OR 45 or Autolite A7. Most are NOS "vintage" spark plugs. Some of the NOS Mopar plugs, especially the ones used in HP engines, Hemi, 340s, 440 HP, command high prices. But....look outside the normal applications....the UJ-11G and the HO-8A Champion plugs I use are for 2 Cycle applications....HO-8A were used in McCullough racing go kart applications and the UJ-11G were for some snowmobile use.....and work very well in my RS23V0A****** but this what works for me.
            BOB RENTON
             
          • Crackedback

            Crackedback Well-Known Member

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            If you don't need to meet any emissions testing and used the "book" timing, throw those numbers in the trash.

            JMO, no mopar should have less than 10-14 initial/idle timing. If it has a bigger cam, up that number. The issue bumping initial timing, you need to tune the distributor so total timing doesn't get out of bounds. Is the carb choke horn black or darkened? That's another symptom of not enough idle timing.
             
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            • 451Mopar

              451Mopar Well-Known Member

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              For Spark Plugs, I would use the NGK XR5, part# NGK-3332 which should be the normal heat range, but they sell a XR4 plug (part# NGK-5858) that is hotter than the XR5.
               
            • steve340

              steve340 Well-Known Member

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              I would bump up the timing as suggested by Crackedback.
              Before you go to a hotter plug there are many other things you need to get right.
              Make sure your fuelling is right at all engine speeds - are the ignition leads spot on?
              Does the engine get warm enough-have you got a thermostat?
              You will foul plugs if the engine is running too cold.
              One heat range hotter than stock would be OK (not more) but be sure it is a fix not a bandaid to cover up something else that is not right.
              I had a 340 that used a bit of oil. I went up one heat range but only on the one cylinder, the rest were fine with the stock plug.
               
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