Tachometer question

**KIRCHNER** · 12-16-2022, 05:27 PM

Will a new 3'' sierra eclipse tach work on a v6 merc 2stroke?

**Onetime** · 12-16-2022, 05:41 PM

Should.
Says it’s for outboard alternator as a source. If you have the Tach in your hands look for a switch to set the signal source. If it has one that says 12 pole alternator you should be good.

**KIRCHNER** · 12-16-2022, 07:12 PM

THERE really vauge with there applications. i have 2, both have the select knob indicators unreadable. 1 reads about double act. rpm other 1 was set for a 4 cyl 4stroke i/o mercruser, i pulled at the boneyard, no markings on the back either. think i could turn it with the mtr running?

**David - WI** · 12-16-2022, 07:39 PM

Not according to the photo on Amazon... It says 4-stroke outboard (2-6 pulses on dial).

https://m.media-amazon.com/images/W/...1Fb3altY7L.jpg

**KIRCHNER** · 12-16-2022, 08:45 PM

Been on the web for 30 min, found only 1 tach with a 12 pulse setting @ 250$. whats up with that..

**Onetime** · 12-16-2022, 08:48 PM

Pretty sure the 6 pulses works.

Click image for larger version.

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**KIRCHNER** · 12-16-2022, 09:30 PM

FARIA says 12

**H2OPERF** · 12-17-2022, 08:35 AM

12 poles and 6 pulses are the same

**PanRonnie** · 12-17-2022, 09:13 AM

Number of ignition events per crank rotation

**25two.stroke** · 12-17-2022, 03:36 PM

Yeah pulses vs. poles ... every tach mfr. labels them different.

IF THE TACH IS ADJUSTABLE THEN IT WILL WORK ON A V6 2 stroke.

Almost all of the tachs made now adays are adjustable: therefore will work. Non-adjustable old ones are what you gotta be careful about. All the new ones with the dial on the back will work; however, figuring the right setting is not always easy. Furthermore, the setting they say in the instructions is not always correct. Always verify with a timing light. I put new tachs in weekly for all sorts of outboards and inboards. You always gotta back check with the timing light.

Sierra says for v6 outboard put it on the 6p setting. I put one in a guy's boat a few months ago as well as changed out 3 reed cages with broken reeds. I set the tach at 6p by the manual and looked up at the tach to eyeball if the rpm was right at idle. It read 700 rpm at idle so I figured that sounded about right. When he picked his boat up and took it out he said it never san so good before...but he only got up to 4800 rpms where before it got to 5500. He asked if the reeds could have caused the rpm loss. I said lemme check something...and took it to the ramp with a timing light. I found it was idling at about 850 where the tach read 700, this discrepancy got exponentially worse as the rpm increased: causing the ~800 rpm issue at the top end. I dropped the tach to 5p and the top end rpm was dead on and the idle was about 50 rpm higher that what it was. Now I don't know if this is just due to bad manufacturing or what, but the moral of the story is the tachs will always work, just you gotta figure the setting.

**KIRCHNER** · 12-18-2022, 01:13 PM

How do you do the timing light thing?

**Onetime** · 12-18-2022, 01:17 PM

If you count the flashes really fast when it’s running!……….Just kidding.

Good question. I’m curious to hear also.

**David - WI** · 12-18-2022, 01:19 PM

Originally Posted by KIRCHNER

How do you do the timing light thing?

Not a regular timing light... https://www.amazon.com/INNOVA-3568-D.../dp/B000EVYGV4

**25two.stroke** · 12-18-2022, 01:44 PM

Originally Posted by David - WI

Not a regular timing light... https://www.amazon.com/INNOVA-3568-D.../dp/B000EVYGV4

I guess I got ahead of myself lol. Yeah...I start a stopwatch and start counting each flash of the timing light. How many times it flashes in the duration of 60 seconds equates to the RPM of the engine...

No. David is right. I use a fancy timing light like the one in that pic. Its the only timing light I ever use so I forget there are more simple ones that are just a light.