I bought an aftermarket small tach (compared to those GIANT 12k tachs) cuz mine went out and i dont want to take the gauge out and i had some o reills money for my bday.

what do i set the cylinder count to. 4 or 6? i assume v6 since thats how many cycles the 2 rotor does...

but anyone know for sure?

 

i feel like an idiot now. my friend sent me this. and i found the same thing soon after.

"The Rotary fires 6 times per one RPM of the rotors (2 rotors x 3 sides). But since the Rotors travel at 1/3 the speed of the crank. The actual RPM you are measuring is the crank speed . Since the Tach signal is reading a single rotor is works out to be 1 pulse = 1 RPM @ the crank) or 1:1 which is the same as a 4 cylinder (4 stroke) motor 1:1."

so pick 4cyl

 

Just compare it to the stock tach for reference if its still installed.

 

Set it to the 4.

 

I'm pretty sure the metal cylindrical thing attached to the outside of the distributor by the vacuum advances has something to do with the tach. If you want to go back to the stock tach try replacing that cylinder thing, its one wire and looks exactly like the one on top of the rear iron over the plate that supposed to have the vin etched in.

 

Aftermarket tach's will work on the 4 cylinder setting off of the trailing coil. That's what we have set up and confirmed it with stock tack prior to removing it.

 

i replaced the whole ignition system and the tach still wont come on. most my gauge are going out anyway and since i have no interior anymore ill just install gauges on the console.

 

well before i got the new tach in i thought. hey, lets put the tach wire (G/Y) from the - trailing to the - leading.

BAM! TACH IS BACK!

how i missed her.

so ill save this aftermarket tach for something else in the future. might be handy if i 13BT a datsun 620 (if i can find one).

 

I guess your trailing isn't working then.

 

it has other things connected to it. both coils are new. but hey. its back and im happy.

today i shall FC water pump housing/alternator swap.

 

So I picked up a Autometer Tach and the setting options are:
4 cylinder - 2 Pulse
6 cylinder - 3 Pulse
8 cylinder - 4 Pulse.

I set the tach on the 4 cylinder - 2 Pulse and tach sort of works. The tach reads 1700 rpm at idle and wont quite reach the 7000 rpm mark.

I have a 1984 12A stockport engine.

Any suggestions?