I have a Yanmar
3JH3E circa 2000. My Tachometer seems to work
(as far as I can tell) up to about 1800 RPM
, then as the engine RPM
increases beyond that the tach starts going down !? I have checked the alternator
belt and it seems good (only 364 hrs on engine
works fine) and replaced the connectors on the sending unit. (I measure .75 Volts there). Have not scoped it yet. What could be wrong ?