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1963 avanti tach erratic

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  • Engine: 1963 avanti tach erratic

    Can any one tell me how to fix the 63 Avanti tach that is iratic when first started and is iratatic with needle jumping
    Joe


    Joe Parsons

  • #2
    The tach sender likely needs rebuilding or replacing. The sender is the round, flat can attached under the steering column and has several wires going to and from it. Several of the vendors carry either reproduction senders or a circuit board that can be installed in yours.
    Poet...Mystic...Soldier of Fortune. As always...self-absorbed, adversarial, cocky and in general a malcontent.

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    • #3
      Try replacing your points, condenser, set the dwell and install new plug wires first. Poor firing can confuse tach signals..
      64 GT Hawk (K7)
      1970 Avanti (R3)

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      • #4
        If a Pertronix electronic ignition is installed, does it contribute to an erratic tach?
        If so, what is the remedy?
        regards,
        Jay

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        • #5
          Erratic avanti tach

          Originally posted by IMJ View Post
          If a Pertronix electronic ignition is installed, does it contribute to an erratic tach?
          If so, what is the remedy?
          regards,
          Jay
          i HAVE INSTALLED THE Pertronix ignition and it worked perfectly for awhile now its is being erratic and jumping around
          Joe


          Joe Parsons

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          • #6
            My tach in the car with a Pertronix ignition acts the same way. But I've only had the car a short time and a previous owner installed the module, so I don't know when the tach got goofy. My Daytona has the dual point distributor and when the malfunctioning voltage regulator took out the tach's sending unit along with every bulb in the car that was lit at the time, I replaced the sending unit with a circuit board that Gunslinger is referencing. But that was for a completely dead tach. I hope someone else can be of assistance as I'm in the same boat!
            regards,
            Jay

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            • #7
              It's not just the old Avanti tachs with a sending unit. I have a new aftermarket S-W tach which does not like the signal from the Pertronix. Do an internet search and most every forum will come up with the same complaint.
              I called them to find out why an old hand held analog Craftsman tachometer
              / dwell meter I have won't correctly display the true engine rpm since
              installing the Ignitor. The engineer was nice enough to spend plenty of
              time explaining how the Ignitor worked and how it differs from breaker
              points.

              He explained that the reason we have so many problems trying to make
              tachometers work with various ignition systems is because tachometers work
              in several different ways in order to figure out the engine rpm. In a
              conventional breaker-point ignition system, present at the negative coil
              terminal is a rising and falling sine wave of voltage potential from pretty
              much zero to maybe 200 volts as the coil is "grounded." Some tachometers
              count these waves or "pulses" to determine the engine rpm by looking for
              the zero voltage portions between some higher voltage. Some look for
              simple rises in voltage or even just the drops in voltage, not caring about
              hitting a zero or any particular peak voltage.

              The problem occurs because modern electronic ignition systems don't
              necessarily have a wave form that matches the conventional breaker-points.
              With a breaker point system, the wave form present at the negative coil
              terminal rises rather rapidly as the points close, reaching a sort of
              rounded peak as the points remain closed for a period and then have a
              tapered tail as the points open and the current is broken (combined with
              the effect of the condenser). In the case of the Pertronix Ignitor, the
              wave form is controlled by the electronics in concert with a capacitor.
              The wave form has a characteristic which includes a very sharp rise, a
              level plateau of 10 to 15 milliseconds (which duplicates the closed points)
              and a exponentially tapering tail. With the ignitor, the voltage never is
              allowed to completely drop to zero. Instead it hits a low of around 1.6
              volts and rises to a high or around 400 volts. This waveform combined with
              these voltages causes the coil primary windings to saturate quickly and
              fully... much more so than breaker-points. This is why the Ignitor is
              capable of assisting the coil in delivering much higher than normal voltage
              output (if needed).

              The dwell in the Ignitor is electronically preset and is not affected by
              the air gap between the magnets and the module (so long as the magnets are
              close enough to the module to trigger the internal Hall effect generator).
              The dwell angle is also not affected by rpm. If properly measured, the
              dwell would be found to be much higher than with breaker-points. A larger
              (longer) dwell is better to insure complete current saturation in the
              coil's primary windings at higher rpms. Fast switching electronic ignition
              systems are capable of delivering this without the mechanical restrictions
              and shortcomings of conventional breaker-points. Mechanical breaker-points
              resorted to dual point systems to extend the dwell.

              So an older tachometer that was designed around the predictable wave forms
              associated with breaker-points may not work at all with a modern electronic
              ignition system. In my case, without a wiring schematic, it's impossible
              to know what the old Craftsman hand held tachometer is looking for to gauge
              the engine rpm. I and the engineer at Pertronix suspect it's probably
              expecting the voltage to drop closer to zero between pulses, so it may be
              counting and averaging several ignition pulses as one. Of course,
              tachometers that are designed around newer electronic ignition systems or
              tachometers which use an inductive pickup work fine.
              jack vines
              Last edited by PackardV8; 04-21-2014, 08:11 AM.
              PackardV8

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              • #8
                Funny thing is that my tachometer doesn't know that! I'm using a Pertonix unit in a Delco distributor and Pertronix coil with the original tach sending unit. The tach gives rock steady performance, as does my clip-on dwell/tach meter. Maybe the electronic tach conversions are too sensitive?

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                • #9

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                  • #10
                    For years I listened to people extol the merits of the different electronic distributors and that they are more trouble free and reliable than the conventional Prestolite and Delco distributors. But in the last 2 or 3 years, I read more and more posts where those who have made to conversion have one problem after another. I have one Stude with a window-type Delco and a dual point Prestolite in my R-2 Avanti. I am careful to do the regular maintenance called for but I have never had any problems and that includes 31 years with my Avanti. My suggestion is that you might want to consider going back to the stock factory setup. But if someone wants to explain to me what I am missing by not opting for all the troubles that seem to come with the electronic distributors, I am all ears.
                    Stan Gundry
                    www.AvantiPublishing.com

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                    • #11
                      Originally posted by Stan.Gundry View Post
                      My suggestion is that you might want to consider going back to the stock factory setup.
                      I have a Lark with the Prestolite dual point dist. I had it rebuilt a couple years ago and I don't mind changing the points. I don't have problems with it or the readings on the tach. If I had the original dual point dist. and it was in good condition for this Avanti, I would be tempted to put it back in. This Pertronix set-up was put in by a previous owner and I'm just trying to get everything to work properly. I don't know if the erratic tach. after start-up is from not enough resistance at the coil or extra voltage from the charging system after the initial drain from the starter. The amp gauge isn't showing an abnormal charging but I haven't checked the voltage immediately after starting yet.

                      regards,
                      Jay

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