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Picture of back of tach please


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Weird that the "calibration" procedure is just turning something "about 45 degrees".  Implies that it's more of a switch, than a calibration.  If it's turned just 35 degrees is the reading off by a small amount or is it back to the 6 cylinder setting?

 

Man, we were mean last month.

 

My 76 and 78 tachs work with a GM HEI module, and a capacitor on the negative post blue wire. Without the capacitor, the needle just quivered.  That was with a ZX coil though, with the HEI module.

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  • 4 weeks later...

Weird that the "calibration" procedure is just turning something "about 45 degrees".  Implies that it's more of a switch, than a calibration.  If it's turned just 35 degrees is the reading off by a small amount or is it back to the 6 cylinder setting?

 

It is a rheostat.  Turning it "about" 45 degrees gets it "about" right.  If you want it accurate, hook up a digital tach and fine tune it until they read the same.  Actually one of the nicer features of the stock analog tach.

 

Mine cuts out when I get above 3-4k RPM.  Just drops to zero.  I've tried two different tachs, adding a tach driver, adding a resistor, powering it right off a battery, everything I can think of.  I even bought a $50 tach with approximately the same sweep and I'm experimenting with installing the guts from it into the stock housing.  It use to work fine with the MSD 6012 box but is getting more and more intermittent.  The cheapy aftermarket works so I know it isn't the ignition, but for some reason I can't get a stocker to work.

 

Might try your capacitor trick.

 

And I've sent enough money to Mike Knell that I don't think he will mind me passing on where the tach adjustment screw is.  Nice guy, a very helpful member of the Z car community.

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