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 Posted: 06-05-2005 12:02 am
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Jim Ketcham
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Location: Salt Point, New York USA
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When I turn my key to the start position (starter cranking) my tach needle rapidly swings up past 8000 and pins.  When I release the key and engine is running tach operates normally.  Does anyone know what is happening here?  I assume I have some type of faulty or misconnection.

I have a Pertronix Ignitor and Pertronix coil and I am not using a ballast resistor.

Thanks in advance for your thoughts on this.

Jim

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 Posted: 06-05-2005 02:25 am
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Judson Manning
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Jim,

The stock ignition system has an additional relay built into the starter.   When you engage the starter, this relay applies 12V directly to the coil (bypassing the ballast resistor).  This gives you a bit more 'fire' on cold start-up.

If the Pertronix coil is like the Lucas 'sport' coil, it has an internal ballast resistor, which means this 'cold start relay' is doing nothing but shunting the ignition lead coming from the tach.

I'd suggest removing both ends of this lead (coil and starter) and cap/tape them off in case you later switch to a coil that needs a ballast resistor.

Judson

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 Posted: 06-05-2005 02:42 am
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Jim Ketcham
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Judson,

THANKS!! You were "spot on".  My Pertronix coil does have an internal resistor so I disconnected the white/yellow at starter and coil ends and tach now works as it should.  A 30 second fix.

You made that easy.

Jim

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 Posted: 06-05-2005 05:16 pm
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Judson Manning
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Glad it helped Jim.

A 30sec fix....maybe...too bad it took me years of playing around with these cars to discover little things like this!

Jensen:  It's not a car, it's a hobby (and/or a way of life)!

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 Posted: 08-02-2005 04:58 pm
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Dan Collier
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Has anyone installed the MSD Tach Adapter PN8920? If I pull one of the white wires from the back of the tach, the engine shuts off which I expected. I checked the purple adapter wire and it does has voltage. I connected the purple wire to the tach and can't start the motor unless I put the original white wire back on. History: I recently converted to the Pertronix ignitor, MSD6A ignition, and MSD coil, I'm getting a tach reading of 2100 RPM and I know the motor is running at about 1000 to 1100 RPM by the sound. 

   Smith Tach

Dan Collier
JH74 14381 2.2L
Jensen-Healey Preservation Photo Gallery

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 Posted: 08-02-2005 07:01 pm
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Mark Rosenbaum
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Haven't installed one myself, but I did look at their circuit diagrams.  The MSD instruction sheet can be found at
http://www.msdignition.com/pdf/8920_frm22049.pdf  .

First of all, verify that the MSD main box, MSD adapter, and Pertronix gadget are all connected exactly as shown on the second page of the instruction sheet, the one that applies to current-mode tachs like the one used in the JH.  Note that for the Pertronix, the black wire is the trigger, and the red wire goes to switched power.  I'm not sure how this is supposed to be done when an MSD box is used, but I'd imagine that their paperwork will explain things.  If not, try the wire from the ignition switch.

Note that the power for the MSD boxes comes directly from the ignition switch and does not run through the tach.  Probably the easiest way to provide this power is to splice into the white wire that runs from ignition switch to tach (NOT the wire from tach to coil).

The MSD coil is connected ONLY to the two wires from the main box.  The ballast resistor is no longer required, and the wire from starter solenoid to ballast / coil should be disconnected and taped off, or even removed.

Once all this has been done, the car should start although the tach will not yet work.  If it doesn't run, then the MSD main box, Pertronix, or coil is bad, or something is not yet hooked up correctly.

Once the car runs, verify that the tach has power on both its Green wire and the White wire from the ignition switch.  The remaining White wire will remain connected to the tach as before.  However, the engine bay end of this wire, which used to go to the coil, will now instead connect to the tach control wire from the MSD adapter box.  The tach will then be driven by the MSD adapter box, which in turn is controlled by the MSD main box, which in turn is switched by the Pertronix device.

If you've done all the above, the tach should work correctly.  If not, call the MSD support line and explain the problem.  If they don't have a simple fix, or if it doesn't work for you, it's likely the tach's internal electronics have degraded due to age and the tach will need to be overhauled by a competent specialty shop, which will need to know the details of your situation.  Alternately, for roughly the same money, you could have your tach's internals replaced with more modern electronics, or install a voltage-mode tach such as those made by VDO.

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 Posted: 08-03-2005 01:26 am
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Judson Manning
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Many years ago I did install the MSD Tach adapter w/ my stock tach.  I've since replaced my tach w/ an aftermarket Automotive tach and run it directly off the MSD6AL tach output.

Not as bad as 2000rpm vs. 1100rpm, but I switched to the aftermarket tach because I could never get accurate tach readouts either.

I just put a 6A in Sander's yellow JH.  We're waiting on the 8920 so we can get some tach, but curiously Sander spoke with an Apps Eng at MSD who said some Smiths tachs need an 'extra' part. 

This mystical part is on its way with the 8920; we'll report our progress...hopefully sooner than later!

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