Nissan NS25C3 2 Stroke 25Hp Tachometer Installation Assistance

csmoczygemba

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Good Morning folks, I have a little 25hp 2 stroke Nissan and I am trying to install a tach. I did a little reading here and purchased the following parts:

3AC726400M TACHOMETER - 4STR - BLACK (FTC8138
3P0726790 TACHOMETER SENDING UNIT
361725390 TACH WIRING LOOM
I understand that the Tachometer sending unit is supposed to connect somewhere near the coil, but the actual wiring colors is not clear to me.

Question 1) Can someone please tell me what colors on the wires go where?

On the back of the Tach, the following wires are present

Black
Blue
Light Green
Red
white
Yellow

I understand the white and yellow are for the tach ground and signal. Can you please tell me what the other wires are for? This particular tach as I understand it is the new one that also contains an oil lamp that I will not be using as I understand that this is for 4 stroke applications. Please note, I believe that the motor is a 1998, electric start, manual choke, remote (not tiller) steering. There are no wires coming out of the remote throttle/shift box and may need additional wires.

Thanks in Advance!
Corwin Moczygemba
 

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Sea Rider

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Welcome to Iboats,

Seems you purchased the wrong tach, for a 2 strokes 25 HP calls for a : 3B7725302 dial tach while the sending unit it's correct. An Induction Tach correctly routed from the motor to the dashboard would have been way cheaper and less complicated to install. What's the idea to count with an installed dial tach for ?

Happy Boating
 
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csmoczygemba

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Feb 18, 2021
Messages
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Welcome to Iboats,

Seems you purchased the wrong tach, for a 2 strokes 25 HP calls for a : 3B7725302 dial tach while the sending unit it's correct. An Induction Tach correctly routed from the motor to the dashboard would have been way cheaper and less complicated to install. What's the idea to count with an installed dial tach for ?

Happy Boating
My understanding, from there here on this board, is that tach is no longer available and that this was the one I needed to buy.
 

Sea Rider

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My understanding, from there here on this board, is that tach is no longer available and that this was the one I needed to buy.
Don't know if a 4 stroke tach will read well installed on a 2 stroke motor unless having a switch in which could select 2 or 4 stroke use. BTW those 25-30 HP fires 2 sparks per revolution and will need to adjust the firing sequence too. Paul should know well for sure...

Happy Boating
 

csmoczygemba

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Feb 18, 2021
Messages
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Don't know if a 4 stroke tach will read well installed on a 2 stroke motor unless having a switch in which could select 2 or 4 stroke use. BTW those 25-30 HP fires 2 sparks per revolution and will need to adjust the firing sequence too. Paul should know well for sure...

Happy Boating
see below from the Tohatsu Website.....the one you suggested is no longer available and they reference the one I purchased. 4 pulses is the proper setting. There is however, no clear wiring diagram.

Notes: /*NO LONGER AVAILABLE. USE 3AC726400M (BLACK) OR 3AD726400M (WHITE)*/
 

Sea Rider

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11,047
see below from the Tohatsu Website.....the one you suggested is no longer available and they reference the one I purchased. 4 pulses is the proper setting. There is however, no clear wiring diagram.
Assume the pulses are referred to as the number of spark plug firings per crankshaft's revolution ? Does the tach counts with other pulse settings aside the 4 mentioned ? If the firing sequence it's not set correctly the tach will read half of double of the actual reading...

Happy Boating
 

csmoczygemba

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Assume the pulses are referred to as the number of spark plug firings per crankshaft's revolution ? Does the tach counts with other pulse settings aside the 4 mentioned ? If the firing sequence it's not set correctly the tach will read half of double of the actual reading...

Happy Boating
I have no idea. but that is what Tohatsu said.
 

Sea Rider

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The Tohatsu guy who answered the phone would be someone sitting at a desk, a technician representative ? My guess would be that a tach meant to work on a 4 stroke motor will not work/read properly on a 2 stroke one, unless capable to program the stroke setting and number of pulses per revolution...

Happy Boating
 

pvanv

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Apr 20, 2008
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You need the sender. Here is the tech bulletin:
 

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pvanv

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The Tohatsu guy who answered the phone would be someone sitting at a desk, a technician representative ? My guess would be that a tach meant to work on a 4 stroke motor will not work/read properly on a 2 stroke one, unless capable to program the stroke setting and number of pulses per revolution...

Happy Boating
Correct, but on "alternator-type" tachometers, the question is number of alternator pulses per revolution. Both 2- and 4-strokes of this size use "wasted spark" on exhaust, so a 4-stroke uses the same tach setup as a 2 stroke.
 

pvanv

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awesome....thank you Paul. Looks like a straight forward hookup.
Easy as they come. I have done them. Fun to breathe new life and accessories into vintage motors. I believe the "sender" adjusts the pulse width to work with the modern setups, since there is no longer the pulser, exciter, and alternator. The C3 only has the exciter.
 

csmoczygemba

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thanks a bunch for the tips. awaiting a new Tach before I mess with it. the one I purchased had a defecting bulb mount and I had to return it. it also has what appears to be an aftermarket temp gauge that I need to fiddle with and get working. The weird thing is that this motor appears to have been a tiller model so it does not have all of the wiring I would have expected at the control box. so...will run a few wires and be done.
 
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Sea Rider

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Interesting alternator type tach install. Bought many moon back that same sender unit thinking that it was some kind of a digital tach, but no, it's just a solid black case with cables and hardware. Is it possible to install the sender and mentioned tach on a non electric start motor with factory alternator installed ?

Happy Boating
 

pvanv

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Yes. Sure is. If you don't have a pulser, but only an exciter, that will work fine.
 

Sea Rider

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Yes. Sure is. If you don't have a pulser, but only an exciter, that will work fine.
Is it possible to install the sender and recommended tach model on 18/30 HP motors with rope start, will you need to count with a power supply say a small motorcycle battery to power the tach for the needle to read ?

Happy Boating
 

Sea Rider

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Going back to your previous post :

Hey there, about to do the same thing on my engine. I have a little aluminum prop on my motor now but will move up to SST.

No need to dump money down the drain going for an expensive SS prop for just a 30 HP motor, an Alum OEM or Solas 11 pitch prop will bump wot revs to max 5800 rpm depending on which type of boat and load the motor will be powering.

Nope, removing the air restrictor won't make the motor to rev higher. It's a combination of : installing a 30 HP air restrictor, advancing the timing advance plate to 25 deg and swapping current 13 pitch prop for an 11 one....

Happy Boating
 

pvanv

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Is it possible to install the sender and recommended tach model on 18/30 HP motors with rope start, will you need to count with a power supply say a small motorcycle battery to power the tach for the needle to read ?

Happy Boating
Yes, you will need power to the tachometer.
 

csmoczygemba

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Going back to your previous post :

Hey there, about to do the same thing on my engine. I have a little aluminum prop on my motor now but will move up to SST.

No need to dump money down the drain going for an expensive SS prop for just a 30 HP motor, an Alum OEM or Solas 11 pitch prop will bump wot revs to max 5800 rpm depending on which type of boat and load the motor will be powering.

Nope, removing the air restrictor won't make the motor to rev higher. It's a combination of : installing a 30 HP air restrictor, advancing the timing advance plate to 25 deg and swapping current 13 pitch prop for an 11 one....

Happy Boating
I prefer a SS prop really for durability....I fish primarily in the bay systems here in texas and it is impossible to avoid the occasional oyster bed or sand bar so Aluminum props get destroyed pretty quickly. My boat is a 16' fin and feather polling skiff that weighs about 300 pounds so with two fisherman and gear, I am likely pushing about 750 pounds. The diameter of the prop drops a little as it has much more mass than the aluminum prop so I am thinking a 10" diameter, 11pitch SST would be just perfect. will toss the aluminum one under the deck as a backup.
 

Sea Rider

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Diameter it's what the prop manufacturer wants to play with, usually not available with the diam one is looking for. Need to have the new tach in working order to wot test a 11 pitch prop as a starter prop from previous 13 one. 750 pounds it's a light feather champ combo, a 30 HP well propped will perform fantastically well...

Happy Boating
 
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