Tachometer

[Mattythemechanic]

Cant get a good tachometer reading. The tach just sits on 7000 when the motor is in idle but the motor is running very quiet so i know its not at 7000. it moves only a hair when i turn the motor off to about 6800 so i think i need a new one because i bought one about 3 years ago used so i think the tach may be bad. My question is can i just go to the local auto parts place and get a regular car tachometer or will that not work with a outboard motor. My motor is a 1975 evinrude 85hp... if i cannot use a car tach can u please give me a link to a tach that will work with this motor thankyou

 

[david_r]

Re: Tachometer

what year, cycle is your motor?

im an auto machanic, but still green on outboards.

but as far as i know the 2 stroke has a different ign system than your car. although im not sure if the 4 stroke has the same as a car.

your tach should zero when you turn on the ign. if not then i would say it is bad. but your tach has a dial on the back that when you set it should be matched to more than just your out of the box tach, just for safety purposes. youd be suprised what a couple hundred rpms will do!

you can buy one here, although i havent priced them, but i know you can get a teleflex from cabelas for bout $60.

but with all the help i get from this site i will definatley spend some of my money here out of appreciation for the help. and joe reeves has a good site also....thanks for all your help joe!

 

[david_r]

Re: Tachometer

and a thank you to everyone else to has helped me, didnt mean to leave anyone out.

sorry again if i offended anyone.

THANK YOU EVERYONE, for your appreciated help and advice!

 

[rickdb1boat]

Re: Tachometer

Make a note of the position of the dial on the back of the Tach. Then turn it back and forth a couple of times. Return it to it's original position and see if it works..

 

[kenmyfam]

Re: Tachometer

Cant get a good tachometer reading. The tach just sits on 7000 when the motor is in idle but the motor is running very quiet so i know its not at 7000. it moves only a hair when i turn the motor off to about 6800 so i think i need a new one because i bought one about 3 years ago used so i think the tach may be bad. My question is can i just go to the local auto parts place and get a regular car tachometer or will that not work with a outboard motor. My motor is a 1975 evinrude 85hp... if i cannot use a car tach can u please give me a link to a tach that will work with this motor thankyou

If it reads 7,000 rpm at idle you certainly have an issue !!!!
As far as I know it should zero out when you turn the ignition on again.
Point of interest, what does it read when you are under way and planing ???? does it move ???

 

[HighTrim]

Re: Tachometer

First off, Im going to assume that the tach used to function until recently. If I am assuming incorrectly, let me know. Tachs have rotary switches on the back that set it to different numbers of coils in the charging circuit, times two because there is a positive and negative pulse for each coil for each cycle. Tachs measure pulses. That being said, you need a tach that has the setting that you need designated on the rotary switch. Yours should be set to 6.



As stated, your tach must ZERO when started. It is easiest to check for 12-volt power and proper ground first. A volt-ohmmeter or 12-volt test light are great tools for this procedure. Simply ground the meter or light, turn the key on and touch the positive probe to the purple wire on the back of the tach. You should see 12 volts indicated on the meter, or if you?re using a test light, its bulb should illuminate. Reverse the leads to check for proper ground, or use the ground wire on the tach to ground your meter or test light. This is likely where your trouble lies, in the ground.

If either the power circuit or ground is the culprit, you can repair the problem and the tach should work fine. In a no-power situation, see if your tach has an inline fuse. These often blow due to constant vibration. After inspecting for power and ground, if it still doesn?t work, it?s time to check the signal-input source, or the tach itself.

A simple way to determine if the tach is bad is to use another tach. Some shops will have a tach ready with alligator clips just for this, ask them and see if they will let you borrow it, or borrow one off a buddy.

In the event you don?t have access to a shop tach, you?ll have to refer to the manual to check the signal source. The signal is a pulse-positive output that?s provided directly from the stator assembly through the rectifier. A peak-reading voltmeter set to ?positive? and the lowest volt scale will enable you to read any voltage output (on this circuit) from the stator.

If everything still checks out, you will need to test your rectifier/regulator.

Let us know how you do.