I've bought a Plastimo tachometer for mi motor. Just wired it up, and started the engine. According to the needle I'm idling at 4000rpm, and doing 7000 at about 5 knots. I don't know if anyone is familer with this sort of tacho, but on the back there is an adjustment thingy which allows you to set how many alternator poles your engine has. I've got mine set to 4 (as per manual). There's also another tiny screw thing which says below it "CAL. Note: do not turn calibration pot poast its limits." Do i need to fiddle with this?
Failing that......do I need to buy something else to make this work. In the tacho instructions it says I need to buy Mercry part no. xxxxxxx. I asked about this is the shop and they said it was just a wiring harness.....