Yanmar Tach.

[billangiep]

Looking for assistance on trouble shooting my tach. Engine is a 3GM with magnetic pick up. At idle it reads correct 750rpm's, as the rev's increase to around 1800 rpm's it reads 1200 rpm's and at 3400 it reads 2200 rpm's. As I increase rpm the gauge responds smoothly. Idea's?
Thanks
Bill,

added edit.....I have removed and cleaned the magnetic pick up and flywheel, checked all conections, wiring from the tach. display head to the mag. pick up and all seems fine.

[Faster]

Two questions:

What are you using to compare the tach to?

Is it possible that the clearance between the pickup and the slug on the flywheel is a bit too much (i.e it doesn't actually always pickup each pass?) This is usually adjustable.

[redcorvette1995]

I have had this problem with my tach 3YM20 on occassion. Happens more often when the tach is cold or it is cold outside. Looking for a fix myself other than total replacement.

T

[billangiep]

Faster, I'm using a hand held contact tach. directly to the front of the crank shaft for testing purposes, There is no adjustment on the magnetic pick up, it bottoms out on the top of bell housing where it is supposed to read each tooth on the flywheel. I figured if the pickup was reading intermittently the gauge would be fluctuating.
Bill,

[Northeaster]

I was looking at buying an aftermarket "Faria" tach (magnetic pickup), as I do not have a stock Yanmar tach (simple panel). I remember reading, on Faria's website, about having to calibrate their tach, by turning an adjustment on the back, (or maybe front), after first selecting how many teeth your flywheel has. (comparing to a handheld tach, for calibration).
I don't know the Yanmar tach at all, but are you sure that there is no adjustment on the tach itself, perhaps on the back of the guage??