TACHOMETER ACCURACY

[phx5kegsman]

I have a 1978 Johnson 115hp V4 crossflow. I'm having issues with my Tachometer. It seems to be accurate up to around 2000 rpm. But, when I push the throttle down tach climbs to around 7200rpms, and I'm not even at WOT yet! I think WOT should be around 5200 on my motor. Obviously, my tachometer is not accurate. Any suggestions WHY?

 

[Berdink]

I know you know your tach may be off, but to check it you can do a loan a tool from AutoZone, or other local auto parts store, and see if they have a timing light with the included tach.
Then at least you'd know how far off it is.
.
In my searching for a tach, I read older ones can be off.
A cheapo inductive one is said to even be more accurate than older factory tachs.

 

[saltchuckmatt]

I have a 1978 Johnson 115hp V4 crossflow. I'm having issues with my Tachometer. It seems to be accurate up to around 2000 rpm. But, when I push the throttle down tach climbs to around 7200rpms, and I'm not even at WOT yet! I think WOT should be around 5200 on my motor. Obviously, my tachometer is not accurate. Any suggestions WHY?

Is this a "new to you" tach? Pulse settings correct?

 

[Chris1956]

Is your prop slipping? Buy a new tach and try it. They do not last forever.

 

[Chris1956]

It probably makes sense to check and clean your wiring to the tach, especially the ground.