Tach reading too high

[TSanders13]

I just installed a new tach on a 40 Merc ('96 4 cyl). It was reading 6700 RPM at WOT. By the sound of the motor there is no way it was turning this many RPM's. Coming out of the whole it was reading 4200 but judging by the lack of whole shot it was turning a lot less than that.(The pitch on my prop is not right yet, part of the reason I'm installing a tach.) I know there is a calibration knob on the back of the tach. What do I need to do to calibrate it? How many RPM's should this motor be turning at idle?

 

[Dunaruna]

Re: Tach reading too high

The calibration knob is usually used to adjust exact zero. There should be switches on the back. What do you have the switches set at?<br /><br />BTW, the tach should have come with instructions about calibration & switches.<br /><br />Aldo