150 HP Johnson Tachometer wrong

ermack

Seaman Apprentice
Joined
Jul 1, 2013
Messages
41
Went out yesterday and my tach is not correct anymore. It is jumping around 5,000 and 6,000 rpm when it should have been around 3,500. It is a 1995. Anyone know where I should start looking to solve this problem?? thanks
 

emdsapmgr

Supreme Mariner
Joined
Dec 9, 2005
Messages
11,551
Re: 150 HP Johnson Tachometer wrong

The tach derives it's signal from the rectifier/regulator in the charging system. If it is not working properly, the tach will act up. Is the charging system working properly?
 

ermack

Seaman Apprentice
Joined
Jul 1, 2013
Messages
41
Re: 150 HP Johnson Tachometer wrong

yes , shows 13 volts when running. seems fine to me.
 

emdsapmgr

Supreme Mariner
Joined
Dec 9, 2005
Messages
11,551
Re: 150 HP Johnson Tachometer wrong

That sounds like the proper voltage when the battery is charged up from running. Usually an erratic tach is due to a faulty rectifier/regulator. If you think yours is ok, it is always possible the tach itself is bad. Try another marine tach.
 

boobie

Supreme Mariner
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Nov 5, 2009
Messages
20,826
Re: 150 HP Johnson Tachometer wrong

You may want to check all the connections going to the tach for being loose or corroded.
 

Barnacle_Bill

Admiral
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Feb 8, 2004
Messages
6,469
Re: 150 HP Johnson Tachometer wrong

Look on the back of the tach and there should be a screw to set it to the number of pulses needed. Yours should be set to 6P. Turn this screw back and forth several times stopping exactly on 6P (close don't count). There are very small contacts inside and over time they can get dirty and this may knock the dirt loose.
 

boobie

Supreme Mariner
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Nov 5, 2009
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20,826
Re: 150 HP Johnson Tachometer wrong

Try what bhile says. I've done this before and it worked.
 

ermack

Seaman Apprentice
Joined
Jul 1, 2013
Messages
41
Re: 150 HP Johnson Tachometer wrong

ok, i will give that a try, I checked all the wires around the rectifier/regulator and cleaned the ground wire there. I will also do the 6p thing on the back of the tach and let you know. It will probably be later this week before I get back out on the water. Thanks
 

ermack

Seaman Apprentice
Joined
Jul 1, 2013
Messages
41
Re: 150 HP Johnson Tachometer wrong

cleaning the corroded wire, and also turned the lilttle thing in the back and it works fine. Now i have another problem, big one i think. I am going to start a new post. thanks
 
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