New tach won't work right

[rbellingar]

Hey there new to this site but not to boating. I've just put a new tach in my boat and it just doesn't seem to respond right. At idle it reads fine then as the rpm's increase the tach increases alot faster. Once the tach hits 5500 it starts to go back down. This is on a 75 evinrude 85hp. The tach is a Faria U.S. Marine set on 12 pole and hooked up to the grey wire in the control box. I've searched the forums and haven't seen this problem so I thought I would see what everyone has to think.

 

[daselbee]

Re: New tach won't work right

Set it for 6 pole.

 

[rbellingar]

Re: New tach won't work right

I thought these motors were 12 pole 6 pulse motors?

 

[Barnacle_Bill]

Re: New tach won't work right

I believe Faria uses pole settings rather than pulse setting so 12 poles would be correct. Test you rectifier. If you are sure it is good and all connection are good you may have a bad tach.

 

[rbellingar]

Re: New tach won't work right

How do you test that just by voltage running and not running?

 

[skippy2235]

Re: New tach won't work right

if you have a 4 cycle engine then:
take the number of poles in the magneto, 12
take the number of cylinders (you dont tell us) =X
Then you take 12 divide by X = pulse number


If you have a 2 cycle engine then:
take the number of poles in the magneto, 12
Then you take 12 divide by 2 = 6 pole

 

[rbellingar]

Re: New tach won't work right

I just finished testing the rectifier and there is no voltage increase at the battery from motor not running to motor running at high idle.

 

[skippy2235]

Re: New tach won't work right

How did the rectifer test out. Is it shorted?
If you are not charging then the tach will not work.

 

[petryshyn]

Re: New tach won't work right

You have a problem with either the rectifier, stator or wiring. Once this is rectified, try the tach again.

If this is a Faria 7000rpm tach, you should be on setting #5.
Note.....Faria recommends a regulator with this application.....