Here are some thoughts:
When the tachometer (Ign. Sw.) is first turned on, pointer must go to
between zero to 50 RPM
<https://www.cruisersforum.com/forums/tags/rpm.html>. If not, check
connections (if OK, tachometer is probably faulty).
Voltages, with engine running should be:
IGN to GND terminal: 12-16 VDC
SEND to GND terminal: 0.3 VAC to 1.2 VAC minimum at idle; (voltage will
increase with engine speed)
The end of the (magnetic pick-up) sender must be within 1/32" -1/16" of
the (flywheel) gear
<https://www.cruisersforum.com/forums/tags/gear.html> teeth, but not
touching the teeth. To adjust, stop engine, loosen the lock nut, and
gently turn the sender clockwise until it touches the flywheel. Back off
(counterclockwise) one turn, and secure with the locknut.
Rust buildup between the flywheel teeth can cause signal loss from the
sender.
I've also heard of voltage regulators causing some variance.
At least a few things to try.
On 2020-10-22 8:47 a.m., David Knecht wrote:
I took the boat out yesterday and at ome point turned on the engine
when the wind died and I needed to manuever. When I glanced down at
the tachometer, it read 4000 rpm. However, from the throttle setting,
the engine sound and the boat speed, it was more like 2000 rpm. I had
run the engine before and all was fine. I ran it later and all was
fine. What might cause a temporary abberant tach reading? Thanks- Dave
David Knecht
S/V Aries
1990 C&C 34+
New London, CT
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