The Yanmar engine panel on my boat has a tachometer originally intended for a 3 cylinder engine and expects 116 pulses per revolution from the sensor which reads the flywheel teeth. As the boat has a 1GM10, and hence only 97 teeth on the flywheel, the tacho under reads.

Does anyone know if it's possible to recalibrate the P116 tacho to effectively make it a P97 tacho?

It's not a big deal as it's simple enough mental arithmetic to factor the error, but I just like things to be right and if it's simply a case of opening it up an moving a dip switch or twiddling a pot, I'll do so. On the other hand, I don't really want to open it up for no good reason if it's known that they cannot be recalibrated.

I rather suspect the calibration is fixed since the tachos are marked on their face to indicate the number of teeth they expect to see per revolution (P97, P116 and another which I forget), although this could just be intended to show what they've been set for internally.

Has anyone tried and succeeded in adjusting one or able to tell me if they are permanently set at component level?

Alternatively, if anyone has an over-reading P97 tacho connected to a three pot engine which needs a P116, I'll swap you.