Tach all over the place

[nmscuba]

I have a 1986 Lund 16 ft tyee that I just purchased with a 1997 Honda 75 hp 4 stroke engine. The tach is all over the place. It might be running at 2000 then for no reason just goes to 6000. When the engine is off sometimes it still shows 900.

I have checked all the wires which are good. I did not find any bad grounds or shorts anywhere.

Is this tach just going bad or is there something else I need to be looking for?

Thank you

 

[Georgesalmon]

Re: Tach all over the place

It's OK for the tach to show 900 or anything else when the key is OFF. It should go to zero when you turn the key on (motor not running). If it does not go to zero with the key ON you have a problem, likely the tach. Since you have checked all the wiring you may have a bad tach. The signal for the tach comes from the stator but if the battery charging system is working OK, the signal is likely OK. Make sure you check the tach signal wire all the way through the control and into the engine where it is usually connected to the input side of the rectifier.

 

[gm280]

Re: Tach all over the place

Is this tach an original or after market? Reason is lots of aftermarket tachs have an option switch on the back side to be able to work with many different engines. That being said, it yours does have such a selector option on the back, try selecting it to different setting a few times back and forth and then reset it back to the initial setting to see if that cleaned the switch contacts and enables it to read correctly again... Those contacts do get some corrosion on them lots of times... Just a suggestion...

 

[nmscuba]

Re: Tach all over the place

yes it is the original Tach from 1986 that lund put in their boats. This boat started with a 2 stroke evinrude and in 1997 went to a Honda 4 stroke.

The terminals are clean and I did not see any adjustment or switch on the back. I will check the wires again back to the motor and see what I find there