Tach readin low

GM165

Seaman Apprentice
Joined
Apr 23, 2015
Messages
34
What would cause a tach to read low? Running at (what I think) is WOT, doing about 35 mph but the tach is reading about 1900 rpm. Moves up and down like I would expect, seems to read idle speed at around 600 okay but I don't think I am only doing 1900 rpm. Boat is new to me. 165hp in line 6 (250) and I haven't really touched it yet except for one quick spin.
 

San_Diego_SeaRay

Petty Officer 1st Class
Joined
Nov 9, 2014
Messages
337
Many times tachs have a setting for 4, 6, and 8 cylinders. You sure yours isn't set on 8 cylinders?
 

thumpar

Admiral
Joined
Jun 21, 2007
Messages
6,138
Check the switch on the back to make sure it is on the right selection for the cylinders. Even if it is move it around and then set it.
 

achris

More fish than mountain goat
Joined
May 19, 2004
Messages
27,468
What would cause a tach to read low? Running at (what I think) is WOT, doing about 35 mph but the tach is reading about 1900 rpm. Moves up and down like I would expect, seems to read idle speed at around 600 okay but I don't think I am only doing 1900 rpm. Boat is new to me. 165hp in line 6 (250) and I haven't really touched it yet except for one quick spin.

Failed tacho?
 
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