Thermoquad low vacuum readings

Fuel and Air Systems

  1. yellow rose

    yellow rose Doctor of Thinkology.

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    So the plugs match your O2 readings? I never go by a number unless it matches the plugs first.
     
  2. midnight340

    midnight340 FABO Gold Member FABO Gold Member

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    Once moving and at most any steady speed whenever I apply throttle (short of opening secondaries) it goes lean off the meter. If I keep accelerating lightly it will stay at 17.5 to 18:1.

    I have old plugs in it and have been trying to get close by A/F meter but have not been checking plugs. Will take a look. I’m going to put fresh plugs in soon.
     
  3. midnight340

    midnight340 FABO Gold Member FABO Gold Member

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    1F7126AB-68D0-496B-B4A0-F7883E54626F.jpeg 2723EB1B-2BF7-4C77-B042-4B40FD70390D.jpeg Here are a couple of plugs. With an otoscope I see I have a medium gray band halfway up the porcelain. (I believe the bottom of the porcelain is mostly WOT?)

    With the Eddy 750 I could barely get any color at the very bottom no matter how big I jetted the secondaries.

    Edit: The plugs are from running 91 octane "real gasoline"...
     
    Last edited: Nov 20, 2019
  4. yellow rose

    yellow rose Doctor of Thinkology.

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    From those pictures, a bit too much total timing and if the fuel ring is half way up the porcelain its rich at WOT.

    The fluffy carbon on the shell means it's a bit rich at cruise.
     
  5. yellow rose

    yellow rose Doctor of Thinkology.

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    Forgot to add, I can't see enough of the plug but from what I can see, that plug is pretty hot.
     
  6. rumblefish360

    rumblefish360 So close, yet so far away

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    Speaking of which, what make and model number plug is that?
     
  7. midnight340

    midnight340 FABO Gold Member FABO Gold Member

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    Timing I believe is still set at 25/37 which netted me highest mph at the last test n tune in October with the old 750 carb. Ran total tests from 33 to 38 but had been been staying around 35 previously. All in around 2000-2200. MPH was not much different with 35 total. (9:1 motor and likes a lot of initial)

    I’ll work on leaning out WOT, give a bit more air by limiting air door a bit (according to some info from demonsizzler posts I found..)

    That is a set of NGK BPR8ES plugs!! Should be too cold but BPR6ES looked too hot for sure. MSD 6 A box.
     
  8. pishta

    pishta I know I'm right....

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    Iirc the dimple in the air door creates a strong vacuum arouns the secondary fuel bar. If you put a smaller jet in the secondaries that should lean out the top end? You could also put a slightly different rod in that has a fatter tip to lean out the primaries off idle. Your idle is spot on. Carter made over 550 AFB models over their life span with different rod combinations.
     
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    • midnight340

      midnight340 FABO Gold Member FABO Gold Member

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      I think your probably right about the plugs looking hot, ...coloring more tha a thread or two. But this plug crosses to a Champion RN6YC. Yes, “6”... so ???

      I tried NGK BPR6ES when everyone said to use 4 or 5’s and they definitely looked hot to me so went to these 8’s.
      It’s things like this that drive me crazy!! :wtf:
       
    • yellow rose

      yellow rose Doctor of Thinkology.

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      I never use the cross reference as a lead pipe cinch. They are at best, a wild asses guess that is right occasionally.

      And...I'm not home to look at my NGK catalog to see what that plug actually is.

      If it is actually a 6 Champion that's a cold plug and something else is wrong.
       
    • midnight340

      midnight340 FABO Gold Member FABO Gold Member

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      Well, I might be off in my understanding of how the heat ranges are listed for this plug. I think I remember a lot of Mopar guys using GR4 and GR5 NGK’s.
       
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      • rumblefish360

        rumblefish360 So close, yet so far away

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        Sorry to ask midnight but did you list what the engine has in it? Cam, compression, headers or not?
         
      • midnight340

        midnight340 FABO Gold Member FABO Gold Member

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        Yes, part of this on page 2 (and I can't blame you for not going back and rereading the whole thread!!! :)
        As a refresh here, I'm trying to dial in the freshly rebuilt TQ 6518.
        Motor is a 1973 9:1 (cc'd/measured) compression 340, LD340 intake, headers, iron X heads fully ported and intake/exhaust port matched, cam is a Lunati 235/243 @ .050, .526"/.546" solid lifter, 2-1/2" exhaust with Magnaflows. Ignition is MSD distr. with 6A box.
         
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        • rumblefish360

          rumblefish360 So close, yet so far away

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          Did you/have you tried the stock plug/heat range for the year vehicle? I don’t remember when the plugs started to get hotter for the emissions years.
           
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          • midnight340

            midnight340 FABO Gold Member FABO Gold Member

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            Yes. Pretty sure I used to use the Champion RN12YC plugs, then switched to Autolite 65's, then started using the NGK's as they seemed a bit easier to read, plus a lot of guys liked them. They all seemed to work, engine ran just fine. I tend to change them fairly often. Edelbrock 750 always seemed on the lean side for this motor, no matter what I did to it. That combined with the MSD kept them clean and looking good. My learning to actually read the plugs is a more recent thing for me.

            As far as timing goes, I always hear the color change should be right at the bend of the electrode, I'll back it down just a bit from where it is now.
             
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            • yellow rose

              yellow rose Doctor of Thinkology.

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              At your CR even that 12 may be too cold. Maybe the picture is tricking my eyes making me think your plugs are too hot.

              There are a ton of plugs Champion makes that even I didn't know about, and, since I'm not home and since the doctors around this crap hole can't get their shit worked tight, I don't know when I'm going home. Plan is tomorrow.

              Once I have my books in front of me, I can see why what I think I'm seeing is wrong.

              Edit: on pump gas the intial timing Mark shoud be almost to the bend and the total mark should be close to the shell.

              Race gas and alcohol read differently.
               
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              • rumblefish360

                rumblefish360 So close, yet so far away

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                I think the plug is to cold. A step or two max IMO will be what your after. But we will see what the engine likes.
                 
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                • yellow rose

                  yellow rose Doctor of Thinkology.

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                  I agree. At first glance it looks hot, but it's easy to get fooled by a picture.

                  That fluffy carbon on the end of the shell may very well be from the plug being too cold. It doesn't have enough heat in the shell to clean off the carbon. If you were running a points ignition we'd be able to see that same type of carbon on the upper end of the porcelain that looks like shadows or clouds. A good ignition takes care of that.

                  That's why reading plugs from a picture is so hard. There is so much to look at and you need to take all that in and get the full look at what's going on.
                   
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                  • midnight340

                    midnight340 FABO Gold Member FABO Gold Member

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                    Tweaked a few things today. I’ve got a set of plugs on the shelf that are two steps hotter. A couple of adjustments by A/F meter then will stick them in and report back.
                     
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                    • midnight340

                      midnight340 FABO Gold Member FABO Gold Member

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                      Installed .110” jets to help with light throttle lean condition and so I didn’t have to screw the rod adjust so high trying to compensate.

                      I decided a part of the problem was the “Industrial” carbs rods had 67/57/45 rods when stock 340 rods are 67/52/45 or so.
                      So I checked my 9000 series parts carbs for rods. Came up with 67/57/54 emissions rods and modified them to 67/52/42. I’ll test all this later.

                      I’ll start a separate thread to show how I made my own rod sizes in case others are interested.
                       
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                      • midnight340

                        midnight340 FABO Gold Member FABO Gold Member

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                        OK, this is a good day!!
                        Back from test runs and some open road. With my new home made rods and the .101 primaries, rod adjust back to 1/1/2 turns, air door 1-3/4 turns. Finally, it's as responsive low and mid throttle as my worked over Edelbrock 750 and stronger pulling at WOT.
                        Got a nice 14.5 mix at idle
                        Out on the road at cruise 14.6-15 or so
                        And no longer going lean at part throttle. At about 1/3 throttle it's 15:1 or a bit under,
                        at 2/3 throttle but no secondaries it will drop to 13.5 so it makes some power.
                        At WOT it will drop to low 11's or even dip into 10's.. I don't know what it is about this motor (or the A/F meter, or O2 sensor) but it really wakes up with these readings.

                        I will now put the new NGK BPR6ES plugs in and see what they say.
                         
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                        • rumblefish360

                          rumblefish360 So close, yet so far away

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                          Woooooo—ooooo... someone is learning!!!!!

                          Nice job! Keep up the detailed reports.
                           
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