Tachometer Setting for a 1977 85hp?

[jdzimmerman]

My tachometer is showing very high RPMs, while idling i am at between 1200 - 1800 and while on the water wide open I am hitting over 6k. The MAX rpm is around 5800 so I really think the tach is set wrong or i have a wiring issue with it. What would be the pulse setting on my motor?

 

[Gomer50]

Re: Tachometer Setting for a 1977 85hp?

If memory serves me right 6 pulse on a 12 pole stator.

 

[jdzimmerman]

Re: Tachometer Setting for a 1977 85hp?

Thanks I will check it out....

 

[jdzimmerman]

Re: Tachometer Setting for a 1977 85hp?

It looks like my Tachometer was factory set to 6 pulses. There is a stamp on the back stating 6GP. I did remove the tech and hook it directly to the motor and I was able to get a reading of 1000 RPMs which is way better than where I was. I then checked the olm readings from the brown Tach wire at the motor all the way back to the mercontrol tach plug and has NO resistance. So in my mind I am good with that lead. I had the same with the motor ground at the same terminal. Next I will check the patch wire from that to the back of the tach. I read somewhere that in order for the Tach to read higher if the pulse is set correctly, it would have to be some electrical interference feeding into the line (not a short). There is a third wire coming from the tach plug on the control. I believe that is power. I guess it is possible that there is some interference there. Will check it out. If anyone has an idea let me know.

 

[Chris1956]

Re: Tachometer Setting for a 1977 85hp?

The tach runs on +12VDC, Ground and the stator signal. Since the brown wire (stator signal) checks out, check the +12VDC (usually white wire) for low voltage and the ground (Black wire)for resistance to ground.

 

[jdzimmerman]

Re: Tachometer Setting for a 1977 85hp?

Got it, but I have one question. The tach has two wires coming from it. yellow which goes to the brown stator signal and a black which goes to ground. What is the white power wire go to? Is that just additional power to the guages maybe for lighting? Enlighten me please! LOL

 

[Gomer50]

Re: Tachometer Setting for a 1977 85hp?

The white wire is for 12 volts + to make the tach function properly.If the Tach has a light it would have a seperate 12 volt supply hook up.At least the ones that I have, yours could be different.

 

[Chris1956]

Re: Tachometer Setting for a 1977 85hp?

If the tach has only two wires, it is the old style and needs to run off the Merc switchbox, brown wire. if it has the three wires, it will run off the stator signal.


What have you got?

 

[chum1]

Re: Tachometer Setting for a 1977 85hp?

You might try one of these tachs,

http://www.northerntool.com/shop/tools/product_524744_524744?cm_mmc=Google-pla-_-Engines-_-Small%20Engine%20Accessories-_-160590&ci_sku=160590&ci_gpa=pla&ci_kw={keyword}

0r here

http://cgi.ebay.com/ebaymotors/ws/e...0562432258&viewitem=&sspagename=STRK:MEWNX:IT

i haven't tried mine yet but will be using to set the rpm on outboards, you cant go wrong with the $19.00 price and its new.

 

[jdzimmerman]

Re: Tachometer Setting for a 1977 85hp?

My tach has 2 wires, when i hook it to the rectifier the tach reads high all the time. So i should try the brown tach wire to the brown switch wire from the trigger?

 

[jdzimmerman]

Re: Tachometer Setting for a 1977 85hp?

That did not work this time the tach read way low. Maybe it needs the 12 volts. i will pull the tach out and see if anything has happened to it. I bought this boat about 6 months ago