TOPIC: Marpac Tachometer Setting Help- 76 merc 1150

Its a Marpac/Faria Tach... Motor is a 76 Merc 1150 Inline 6

Problem I am having is when idling the motor, the tach will bounce from around 900 to 2000rpm. Some settings will give it a much higher reading than what it really sounds like. I've tried a couple different settings on the tach, but they are all different. Which one should I have it set at? The label on the back looks like this.

#of Cyl or Poles Set
4 1
6 2
8 3
10 4
12 5

I was told to have it set at 6 PULSE.... Set on 5 poles it doen't work.

I believe you will need to turn the pointer to the number 2 setting, cturbo.

MarkS wrote:

I believe you will need to turn the pointer to the number 2 setting, cturbo.

Agreed, you may also have to move the tach input wire from the switch box directly to the terminal of the rectifier. Connect it to one of the yellow wires coming from the stator to the rectifier.

It is on the rectifier tied sharing a terminal with the stator. It bounces pretty bad at idle and sounds lower than the tach readout. I'm going to try a couple things today..
Go to about the five minute mark in this video and you'll see.

Well, I just looked my Faria tach that quit working. Motor that the "Doc" built for me. 72 115 rebuilt to a 135. I even got 2 of this tachs and gave one to Thom. For what its worth, set at #5, 12 pole.

Robby321 wrote:

Well, I just looked my Faria tach that quit working. Motor that the "Doc" built for me. 72 115 rebuilt to a 135. I even got 2 of this tachs and gave one to Thom. For what its worth, set at #5, 12 pole.

Thats what I'm gathering from Thom and some others. I'm wondering why at 5 it does nothing? It will jump to zero when the key is turned, but nothing when its running. I'm going to take another look at it, and double check my rectifier i guess?

could be a bad charging system

dave bernard wrote:

could be a bad charging system

Well... I haven't tested the rectifier itself but the other day when I had it idled up high (not sure due to malfunctioning tach) it was putting back at the battery 15v.

[thats what I'm gathering from Thom and some others. I'm wondering why at 5 it does nothing? It will jump to zero when the key is turned, but nothing when its running. I'm going to take another look at it, and double check my rectifier i guess?[/quote]

If the tachometer goes to zero when you turn on the key you may have a bad rectifier allowing voltage from the battery, back through the rectifier and the stator to the tach.

Well, my Faria tach seemed to read high too. Can't remember if it bounced though. All I do know is it didn't last long at all. Simple quit altogether. I think Thom had trouble the one I got him too. I went and bought a new Merc Tach, and although seemed to read high at idle, solid and seemed WOT is correct.
Simple could be a bad tach ya got. The new one in my big boat quit working after a year too. I simple HATE electrical stuff! But I'm pretty good at "letting the smoke out wires though!"

Wellll... I guess its off to test the rectifier then. And then replace tach if all goes well...

Daveswaves wrote:

[thats what I'm gathering from Thom and some others. I'm wondering why at 5 it does nothing? It will jump to zero when the key is turned, but nothing when its running. I'm going to take another look at it, and double check my rectifier i guess?

If the tachometer goes to zero when you turn on the key you may have a bad rectifier allowing voltage from the battery, back through the rectifier and the stator to the tach.[/quote]

Dave, I think your on to something here..(and he forgot more then I will ever know too, and the Doc takes is word as gospel real"

When ya shut down the motor, the Tach should stay last rpm. I just went out to my Flat bottom and shoved the key in...(its still pickled from winter too), and the Tach barely moved last shut off ignited. No fast "Zero"

Tell us, is this a new bought Tach, or original?
But still think Daves on to something here...

It was a tach given to me from a pal. Back when I started my restoration, I had an Evinrude on the boat and the only gauge was an old tach mounted to the dash. So it is not new, nor original. Its used, but doesn't look in bad shape.
I can change the setting on it to something else, and it will function. But set on 5, i get nada.

Okay.... Its fixed. and I didn't have to buy anything.

With some suggestions from you guys and Dr Frankenmerc...
Tested stator- Good.
Tested rectifier- good.
Cleaned rectifier connections and swapped wire to other stator wire.

Rotated dial back and forth on tach and set to #5!

Wala--- Fired her up, tested for proper voltage, and watched the tach needle stop bouncing....

Thanks for the help!

HA!..Saw the "Doc" yesterday!" We sure got some "wizards here right?

"With some suggestions from you guys and Dr Frankenmerc...?"

This...(as all in the signal!)

Cleaned rectifier connections and swapped wire to other stator wire.

Rotated dial back and forth on tach and set to #5!


Good Luck the old Merc!

Lucky dog..... That's my main man there. He actually walked me thru my entire rebuild and I did it all in my backyard with no garage.
Now- time to mount seats, cleats, put on reg stickers, kick the tires, and light the fires....

And figure out where I want to splash her for the first time.