Frequently Asked Question
Tachometer is erratic (4-stroke engines, engines with magnetos or electronic ignition)
Last Updated 2 years ago
Problem : Tachometer is inaccurate, reading a fixed percentage too high or low at all RPMs, although it is steady.
Almost certainly you have the TachP/R ( in very old instruments, the EMP) set incorrectly. When sensing engine RPM via the mag P-lead, it is common for a mag to generate ½ as many pulses you expected. (A mag for a 4-cylinder engine, would be expected to produce 2 pulses per revolution, but it might produce only 1.) See the user manual for the correct setting.