Inaccurate tachometer

[sadil340]

When I restored my 70 Cuda 340 I send the instruments out to be calibrated and resurfaced and converted the car to electronic ignition. Ever since, the tachometer reads high by a few hundred rpm. Is it the controller or the tach that is causing that? Any suggestions as to how to troubleshoot would be very helpful.

 

[pschlosser]

Over the years, I don't recall seeing ANY tachometers in rallye dashes accurate to less than 100 RPM. While I know little how to calibrate or fine tune the tach, a few hundred RPM off is pretty common and easy to live with.

When I set idle speed, idle mixture, and other ignition timings, I use an external "tune-up" tachometer that reads pretty accurate.

 

[Deathproofcuda]

When I restored my 70 Cuda 340 I send the instruments out to be calibrated and resurfaced and converted the car to electronic ignition. Ever since, the tachometer reads high by a few hundred rpm. Is it the controller or the tach that is causing that? Any suggestions as to how to troubleshoot would be very helpful.

Do you know if your tach is using the original circuit board or has it been upgraded to use newer electronics, like the ones from Real Time Engineering? RTE offers a replacement circuit board with a calibrator built into it.

67-74 Tach Board with Calibrator Built In - rte

So there may be a way to recalibrate your tach, but you would need to know what circuit board your tach is using. I'd check back with the gauge shop that you previously used.

 

[Rons340]

I rebuilt my tach and was able to calibrate it using the tach on my timing light and the instructions provided by the supplier. I have included a link below for the service information. Page 3 references the calibration procedure.

OEM-Style Mopar Tach Board Installation Instructions