wiring in a tach?

[Billy Ricks]

Tachs have three wires. One signal that goes to a coil, one power supply and one ground.

Not sure about the tach you've chosen, but here's hoow mine is wired. The black wire with the red tracer on the GSX-R tach is the signal wire. Hook it up to the black/yellow wire from your ignitor. The black/orange wire on the tach is positive power and the black/white tach wire is ground.

Hook the ground up to its own supply. At first I had mine hooked up to a cluster of grounds and the tach would go to 7000 rpm for some reason as soon as the key was turned on. Once I gave it its own ground the tach worked right.

[Anonymous]

on a newer car the tach probably goes into the computer because it know when to fire each cylinder and it would be completly accruate ...but on a older car with a distributer do the engines have a waste spark like ares do, like spark on exaust to because that thing that goes around doesnt it spark every cylinder at top dead center or only when needed i would think its waste spark cuz it turns around in a small radius but im not sure........i went to canadian tire and they had some nice small tachs but the guy said there for 4-6-8 cylinder so theres no way to make it work on a twin?

[Billy Ricks]

If you go with a tach set up for a four cylinder car engine it should count right for a two cylinder firing each stroke.

[gtsg01]

I took these readings on my bike!!!

Here is the result of my Dwell/Tach test on my GS1100.

Meter connected to the White wire of the 1-4 coil.

Engine idling at 1000 rpm indicated on mechanical tach

On 8 cyl scale = 250 rpm

On 4 cyl scale = 500 rpm

On 2 cyl scale = 1000 rpm

These readings are from an analog meter and are approximate, but in the ballpark.

The 4 cyl GS engine has 1 pulse per rpm. So you need a tach with a 2 cylinder setting.

I was quite surprised at the results. I have tried to work it out in my head and always came up with 2 pulses per rpm

Most of the inexpensive Tach's I have seen only have 8-6-4 cylinder settings.

[Anonymous]

Your tach has a 2 cylinder option on it? or did u just figure out what would it be for a twin?.....Any ways if you have a tach for a four cylinder im pretty sure all u gotta do is connect the wire from the tach to both coils. FOUR cylinder bikes and TWINS have two coils so there the same when it comes to tachs. So if it was indicating 500 on one coil just connect it to both coils and it should be right. It would get the correct amount like it would in a car. Why would it show a higher rpm for a twin if you connected the tach to one coil on a twin and another on one coil of a 4 cylinder gs both with a waste spark ignition it would be the same.

[Anonymous]

Your tach has a 2 cylinder option on it? or did u just figure out what would it be for a twin?.....Any ways if you have a tach for a four cylinder im pretty sure all u gotta do is connect the wire from the tach to both coils. FOUR cylinder bikes and TWINS have two coils so there the same when it comes to tachs. So if it was indicating 500 on one coil just connect it to both coils and it should be right. It would get the correct amount like it would in a car. Why would it show a higher rpm for a twin if you connected the tach to one coil on a twin and another on one coil of a 4 cylinder gs both with a waste spark ignition it would be the same.

If you connect the wire from the tach to both coils you are, in effect, connecting the negative side of both coils together. You cannot do this.

[gtsg01]

If you connect the tach to both coils, you will not only have a tach that doesn't work, but an engine that won't run!

Shorting the two coils togegther will cause them both to fire at every trigger point. This will cause backfiring and most likely cause engine damage. It could also take out your igniter as well.

You should go ahead and try it, "ON YOUR BIKE"

My Dwell/Tach Meter is an old Sun unit and it has a 2 cylinder setting on it.

[Billy Ricks]

I finally got the dwell/tach readings straight in my head and they make perfect sense.

[Anonymous]

I finally got the dwell/tach readings straight in my head and they make perfect sense.

I was hoping I didn't have to come down there!

[Anonymous]

now that i think about that , i guess i wasnt thinking at the time...but Really what i meant is if there was a way to do it it would then be accurate. Lets say the tach had two wires on its own or if there were some kinda thing you could get from radio shack to soldier in between the second wire so they wouldnt interfier .....you know what i mean if there was a way it would work nicely.

[gtsg01]

Not Happening!!

[Anonymous]

tach install

All this tach talk inspired me to re-register on the site. I am the tech support manager at Auto Meter, and now you guys have me confused! Basically, most Japanese 4 cylinder four strokes end up being 2 pulse/crankshaft revolution at either coil, H-D's and most other V-twins are one pulse/rev, and there are some less common variations. The only time we have used the 9117 adapter on a bike is when doing an install on a very late model H-D such as a V-Rod, which uses a data bus or multiplexed electrical system. I have never tried one of our tachs on my GS750, but will play with it a little shortly. Regardless, I would like to send you a tach for the price of giving me some feedback on how things worked out., and maybe a photo of the install. Let me know if you are interested.

[Anonymous]

Re: tach install

All this tach talk inspired me to re-register on the site. I am the tech support manager at Auto Meter, and now you guys have me confused! Basically, most Japanese 4 cylinder four strokes end up being 2 pulse/crankshaft revolution at either coil, H-D's and most other V-twins are one pulse/rev, and there are some less common variations. The only time we have used the 9117 adapter on a bike is when doing an install on a very late model H-D such as a V-Rod, which uses a data bus or multiplexed electrical system. I have never tried one of our tachs on my GS750, but will play with it a little shortly. Regardless, I would like to send you a tach for the price of giving me some feedback on how things worked out., and maybe a photo of the install. Let me know if you are interested.

You would get 2 pulses/revolution of the crankshaft if there was only one coil.. With 2 coils and 4 cylinders, each coil fires once per revolution. Each cylinder at tdc compression and tdc exhaust.

Funny you should mention H-D's. Their ignition system is basically 1/2 of the GS's - 2 cylinders and 1 coil vs. 4 cylinders and 2 coils. I'm not sure about a V-Rod, but if they have individual coils for each cylinder then they would need the 9117 adapter.

Pretty simple really.

If you are serious about sending a tach for feeback, I don't think you would find a shortage of applicants here.

[Anonymous]

tach install

Yes, I would like to get one or two tachs out to members willing give me some photos and feedback. And you are right, unlike some other inline fours, my '78 GS 750E is one pulse/rev based on only one lobe at the points end of the crank.

[earlfor]

I installed a Nordskog digital memory tach (NRD-M9004) from Summit last year. It operates on one pulse per revolution. My Dyna ignition has a selectable tach drive pulse rate, so it was easy enough. :-) I removed the stock tach from the 1150E instrument cluster, made a carbon fiber face plate and recessed the digital tach inside the cluster for a stock appearance. It has worked flawlessly.

Earl