Auotmeter Tach

[TwoJugs]

I am in the slow process of getting the old XS drag bike back on the strip. Looking for a tach to use and found an Autometer 3690 that might? work. Called the company customer support and they were pretty clueless with info that would lead me to believe it would. Just stated that it works with "some" 2 cylinder motors. Being that the XS has more of a 1 cylinder ignition set up, times 2 not sure if it will work. Anyone had experience with this? I can't wait to get the shift light in my eyes.

 

[grizld1]

You need to know more than number of cylinders. An XS650 ignition that uses two separate coils (OEM breaker point ignition, for example) needs a tach calibrated for 0.5 pulse per revolution. Single coil waste spark systems (OEM TCI, Probe, Boyer, Pamco, etc.) need a tach calibrated for 1 pulse per rev. Many aftermarket electronic tachs allow you to select calibration. Acewell instruments have gotten pretty pricey--almost double what they were 2 or 3 years ago. Check out the Vapor tach/speedo from Trail Tech.

A common problem with aftermarket electronic tachs is spiking due to electronic "noise". Hook up the sensor wire direct to the coil primary negative, and if the reading spikes, add a 1 megohm resistor to the wire right after the coil. If it still spikes, add a second 1 megohm resistor.