Inaccurate tach on my 1968 Evinrude Sportsman 155

[Volvowayne]

I am new to this board and my boat (2nd season) however, I have been a boater all my life and always worked on my own equipment.
My boat has the original Buick odd fire 225 V6 and the original tach in the dash. The mystery is that the tach read much higher RPM's than the engine is turning. For example, just barely off idle, traveling say 10-12 mph the tach is reading 4500 RPM's. Crazy.
What are your ideas about fixing this? What could be going on being that all the equipment is all factory original (as best as I can tell)?

 

[swaycleveland]

If you can get a timing light with a tach built in you could verify. you can also use a multi meter with one built in. those are the most common ways. also just to be clear. Your engine is a v6 3.8 with the distributor in the back or front. If its is in the back it is NOT a buick. It is still a gm engine. but a chevy which is more likely. I personally havent seen a 3.8 buick (front dist) in a boat.

 

[swaycleveland]

also there commonly a switch on the back of your tach in the dash. that switch controls the reading 4 cyl 6 cyl 8cyl check that also

 

[Bondo]

I personally havent seen a 3.8 buick (front dist) in a boat.

Ayuh,.... I have, they're out there, just few, 'n far between,.....

Welcome Aboard Wayne,.... That tachs pretty old,... Have ya tried just thumpin' it with yer fingers,..??

I've had 'em come back to life that easy,....

Switchin' the switch on the back around also knocks 'em back into shape, as noted above too,....