Duke! Some help with "afterburn" please - Update - NCRS Discussion Boards

Duke! Some help with "afterburn" please - Update

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  • Gary Wilkerson

    Duke! Some help with "afterburn" please - Update

    I finally got a chance to look at the 66 and further investigate by muffler mishap.
    General concensus was my test plan was sound so here goes the inital results and some interesting findings:

    Cyl------------Plug--------Wire (Ohms) Compression (Lbs)
    1------------Little Sooty-----1502------------210
    3------------Little Sooty-----1425------------215
    5------------Little Sooty-----1100------------218
    7------------Less Sooty-----1039------------220
    2------------Little Sooty-----1421------------206
    4------------Greyish/Tan----1264------------210
    6------------Little Sooty-----1285------------212
    8------------Greyish/Tan----1144------------206

    Wire resistance is fairly consistant concidering length of each so I don't think that an issue. Compression is low on a couple of cylinders, but I don't know if I should be alarmed.
    The engine was running eratically (similar to an inconsistant mis or multiple cyl. misfiring)at idle. I decided to check the timing. Before removing the vacuum can hose I checked timing with a light. The timing mark was bouncing around at least ten degrees. At that point I diconnected the can and engine smoothed out.
    Initial timing was set at apprx. 10 deg so I changed that to 5. The engine still ran smoothly until I connected the can again and it ran erratically.
    I connected an old vac can and saw that the rod was indeed moving in and out.
    I decided to make a complete check of the dist. and the vac at the intake. Vac at the intake was about 14
    When I pulled the dist cap I saw the tab on the rotor button (the one on the outside of the rotor button)was not pointing straight out but at approx a 22 deg angle. The plastic on the side of the tab was broken which allowed it to spin. The rivet was still pretty solid so I straightened the tab and readjusted timing, idle speed and idle air adjudtments.
    It seems to run smoothy now even with the can attached. It still seems to run rich however, I think thats attributable to the 3310 carb.

    Any and all comments are welcome.

    Gary
  • Craig S.
    Extremely Frequent Poster
    • June 30, 1997
    • 2471

    #2
    Re: Duke! Some help with "afterburn" please - Upda

    Gary - you pretty much self diagnosed your problem, the rotor should be replaced with a new one for sure. The compression readings are somewhat high across the board, but this is probably due to your cam, i am used to the hi-perf cams with less dynamic compression. The cylinder to cylinder variation is fine. You may still have an over rich condition in the 3310 to sort out, but other than that,you sound like you solved your problem. I would check the advance weights and bushings under the rotor when you replace it for any overly worn conditions, and set up the vacuum can with a full manifold vacuum setup as Duke has described before.... Craig

    Comment

    • Gary Wilkerson

      #3
      Re: Duke! Some help with "afterburn" please - Upda

      Craig, thanks for the feedback. I am going to replace the rotor, most probably the cap as well.
      I'm looking for the correct 3370 carb to replace the 3310, so when I find one I'll hopefully fix that condition.
      As for the vacuum. Do I understand that I should ensure I'm using a can that fully pulls in at full manifold vacuum? In my case that looks like 14.

      Gary

      Comment

      • Craig S.
        Extremely Frequent Poster
        • June 30, 1997
        • 2471

        #4
        Re: Duke! Some help with "afterburn" please - Upda

        Duke has had some great posts on the vacuum can to use, NAPA 1810 for SB and 1765 I think for BB (at least for the 427/425 like my 66). It somewhat varies based on the advance curve of the distributor, but the idea is to avoid the ported vacuum on the carb which was used as a pollution control measure, and it caused hot running and high exhaust temps at idle with associated overheating. Somewhere in the archives there are great posts on this......Craig

        Comment

        • Gary Wilkerson

          #5
          Re: Duke! Some help with "afterburn" please - Upda

          Thanks again Craig. I'll take a look.

          Gary

          Comment

          • Craig S.
            Extremely Frequent Poster
            • June 30, 1997
            • 2471

            #6
            Re: Duke! Some help with "afterburn" please - Upda

            Gary, I may have them saved in a file too, with many other posts.......I can't recall, was your engine a 427/390 or a 327? If you email me so I have your email addy, I would be willing to forward my saved post file but you may be sorry Craig

            Comment

            • Duke W.
              Beyond Control Poster
              • January 1, 1993
              • 15649

              #7
              Re: Duke! Some help with "afterburn" please - Upda

              Compression numbers seem high, but consistentcy is what counts, and it is there!

              It appears you have two different vacuum cans that you are swapping back and forth???

              The OE spec vacuum can is suitable for the engine and you should make sure that it is in spec.

              Total idle timing should be the sum of initial and full vacuum advance. Check against specs, and the engine should pull at least 16" at 600 idle in neutral, and it should have a smooth idle.

              The carburetor may certainly be an issue. A 3310 is a "one size fits all" aftermarket version and is probably not well suited to many OE conversions.

              Duke

              Comment

              • gary wilkerson

                #8
                Re: Duke! Some help with "afterburn" please - Upda

                Thanks Duke,

                I'll double check the can to see if it's in spec. You're right about the carb I'm looking for the correct 3370.

                Gary

                Comment

                • Wayne M.
                  Expired
                  • March 1, 1980
                  • 6414

                  #9
                  Your Plug Wire Resistances seem Low

                  If you assume about 5000 ohms per foot for resistance wire, small block plug wires for cylinders # 1,2 and 3 should read about 18K ohms (~43"); cylinder # 4 @ 17K; cylinders #5 and 6 @ 10K (~25"), and cylinders # 7 and 8 @ 9K (~22"). Chilton's manual says wires should be replaced if higher than 8K ohms/foot.

                  Now I'm no electrical engineer, but is it possible that your low wire resistances are inducing X-firing between cylinders ?

                  Comment

                  • William C.
                    NCRS Past President
                    • May 31, 1975
                    • 6037

                    #10
                    Re: Your Plug Wire Resistances seem Low

                    Actual spec for the resistance wires had a broad range I believe 2500-4000 ohms per foot. The LR designation on the wires represents "Low RESISTANCE" as opposed to some stuff made for Chrysler that ran 4500-6000 per foot (approximately)
                    Bill Clupper #618

                    Comment

                    • Gary Wilkerson

                      #11
                      Re: Your Plug Wire Resistances seem Low

                      Wayne,

                      I just purchased this car. I'm trying work the initial bugs out of it. It came with a set of new Accel 8MM monster core wires. They seem to be in excellant shape. But I'm not sure what the Ohm/Ft is supposed to be.
                      I do have the stock wire mounting and separators. I don't think I'm seeing cross firing between cylinders

                      Gary

                      Comment

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