[C320-list] Tach running high

[Troy Dunn]

Jeff is correct, there is a calibration screw on the back of the tach.   If
it hasn’t been tampered with or "adjusted" it will have a sticker across it
with some language like "don't mess with this screw".   If your tachometer
is getting long in the tooth there are a few things to check before you
recalibrate the tach.

1.  There is a ground wire and a sending wire attached to the sensor which
sits on the back of the engine near the transmission.  Remove these spade
terminals, cut off the terminals and reterminate the wires.   The yanmar
harness is not marinized, it is copper wiring that has not been tinned.
Over time moisture wicks up into the wiring through the non-marine
connectors and corrodes.   This is true of all the terminations on the
engine, so the same advice applies to all misbehaving senders and switches.
(Oil, temp, etc.)

2.  While you are at it, check that the ground wire from the sender is
attached to a good ground.  The grounds are all terminated on one of the
bolts for the starter.   Remove said bolt and check all ground
terminations.   At a minimum, get some sandpaper and clean the ring
terminals.   Better to just reterminate with proper adhesive lined heat
shrink ring terminals.  When putting grounds back in place, remember larger
terminations against the engine block first.  Some engines will have a
secondary ground point near the mounting bracket near the tach sender.
Stack them biggest to smallest from the block out, reverse order if you are
stacking on the bolt.

3.  If your tach 'bounces' around, you can probably get this to stop by
turning the calibration screw back and forth a few times to wipe clean the
contact surface inside the gauge.   Just be sure to get the screw set back
to the same position it was in, unless of course you are going to
recalibrate and have a flywheel pickup on hand to do so.

Good luck-

Troy Dunn
Hull#514