[C320-list] Tach running high

[Michael Leschisin]

So, one of the easiest fixes I’ve made on the boat….

Before starting the engine I wiggled around the tach pickup wires, based on Troy’s photos, just to see if anything was loose.  There didn’t seem to be any unusual play in the wires so I started up and idled the engine.  The tach displayed its normal 1000 RPMs.  Maybe a bad connection?

Thanks for everyone’s input.


Michael Leschisin
Wild Blue Yonder
2004 C320 #995
Menominee, MI




> On May 31, 2024, at 6:59 AM, Arthurpiotrowski via C320-list <c320-list at lists.catalina320.com> wrote:
> 
> Hello, had a somewhat similar issue on our “Maggie”, #330. Solution was to clean the leads of the tach wire, back of the engine, access from the aft berth. 
> 
> Sent from Artur’s phone
> 
>> On May 31, 2024, at 7:16 AM, Troy Dunn via C320-list <c320-list at lists.catalina320.com> wrote:
>> 
>> 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
>