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wiring in a tach?

  • Thread starter Thread starter Anonymous
  • Start date Start date
gtsg01 said:
If I may offer a suggestion. While everyone seems to have a grasp on the number of pulses per revolution, you only need to monitor One coil to get the tach to work properly.

So, if you hook the tach to the 1-4 or 2-3 coil and set the tach to 4 cylinders, it should read correctly.

I will hook my dwell/tach tester (Yes, I am an old fart and still have one) to my 1100 this afternoon to verify.

I will let you know how it turns out.
Click to expand...

That is exactly what I was thinking. However. How would you go about wiring the tach into the coil?
Explain please, I plan to pick an electronic one up after work today.

Thank you,
Dm of mD
 
Automotive tachs just connect to the negative side of the coil. I was talking about only using one coil as well, but hadn't been aware that they fired on compression AND exhaust.
 
So, what's the prognosis here? Still deciding?


Billy Ricks said he wired in a GSXR Tach, how hard is that and how much configuring is needed?

Sorry to hijack, but sounds like lots of Tach trouble going around. :?

Thanks
 
fastpakr said:
Automotive tachs just connect to the negative side of the coil. I was talking about only using one coil as well, but hadn't been aware that they fired on compression AND exhaust.
Click to expand...
That's correct - wire to the negative side. If an automibile has 8 cylinders and one coil it fires 8 times for every two revolutions of the crank. A 4 cylinder car fires the coil (single coil) 4 times for every 2 revolutions. The GS fires each coil 2 times for every 2 revolutions or 1/2 the count for a 4 cylinder tach wired to the coil. You then get 1/2 the RPM reading on the tach.

If you are using a tach that reads from a single coil for each cylinder, then you will get an RPM reading of 2x since the GS fires for 2 cylinders.

It all depends on how they indtend the tach to operate in the first place. Put it on and look at it.
 
So you would have to run the tach negative to the negative on both coils right?

(I'm so confused by this electronic tach theory)

:(
Dm of mD

Swanny said:
fastpakr said:
Automotive tachs just connect to the negative side of the coil. I was talking about only using one coil as well, but hadn't been aware that they fired on compression AND exhaust.
Click to expand...
That's correct - wire to the negative side. If an automibile has 8 cylinders and one coil it fires 8 times for every two revolutions of the crank. A 4 cylinder car fires the coil (single coil) 4 times for every 2 revolutions. The GS fires each coil 2 times for every 2 revolutions or 1/2 the count for a 4 cylinder tach wired to the coil. You then get 1/2 the RPM reading on the tach.

If you are using a tach that reads from a single coil for each cylinder, then you will get an RPM reading of 2x since the GS fires for 2 cylinders.

It all depends on how they indtend the tach to operate in the first place. Put it on and look at it.
Click to expand...
 
Swanny, I really think you're mixing yourself up in that logic somewhere. Using the info you just gave that the GS justs divides the job across two coils (but total pulse count is no different from a single coil auto system that fires each time a cylinder is coming up on compression stroke), then the coil reading of a single coil on a GS will be 1/4 that of the only coil on a typical 8 cylinder car. To get the readings to match, you'd need an auto coil for a 2 cylinder car (yes, i realize that's not going to happen).

That is, unless each coil on a GS fires every time either of the cylinders it powers is on the compression stroke, as some others seem to be indicating?

random numbers...
8000rpm = 64000 pulses/minute (8 cylinder, single coil)
8000rpm = 32000 pulses/minute (4 cylinder, single coil)
8000rpm = 16000 pulses/minute PER COIL (4 cylinder, 2 coils)
8000rpm = 16000 pulses/minute (2 cylinder, single coil)
 
Correct me if I'm wrong here guys but......

If you look at the pickups you'll get some idea of how it works. There are two pickup coils and one rotor. Every time the rotor passes a pickup it sends a pulse to the ignitor.

This means two pulses per crank rotation.

The Ignitor sends out one pulse per crank rotation to each coil, ergo each spark plug gets a jolt every time it passes TDC, therefore each coil gives out the same number of pulses as the crank revolutions.

The reason I need to put a frequency divider in is that I've fitted a Boyer branson electronic ignition to my GS550ES. The rotor arm on this has two magnets and the pickups wired together in series which effectively doubles the pulses sent out to the ignition module. Which means each sparkplug gets a whack on every half crank revolution.
 
Detman101 said:
So you would have to run the tach negative to the negative on both coils right?

(I'm so confused by this electronic tach theory)

:(
Dm of mD
Click to expand...
You can't do that.
 
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.
 
fastpakr said:
Swanny, I really think you're mixing yourself up in that logic somewhere. Using the info you just gave that the GS justs divides the job across two coils (but total pulse count is no different from a single coil auto system that fires each time a cylinder is coming up on compression stroke), then the coil reading of a single coil on a GS will be 1/4 that of the only coil on a typical 8 cylinder car. To get the readings to match, you'd need an auto coil for a 2 cylinder car (yes, i realize that's not going to happen).

That is, unless each coil on a GS fires every time either of the cylinders it powers is on the compression stroke, as some others seem to be indicating?

random numbers...
8000rpm = 64000 pulses/minute (8 cylinder, single coil)
8000rpm = 32000 pulses/minute (4 cylinder, single coil)
8000rpm = 16000 pulses/minute PER COIL (4 cylinder, 2 coils)
8000rpm = 16000 pulses/minute (2 cylinder, single coil)
Click to expand...

Corrected random numbers...
8000rpm = 32000 pulses/minute (8 cylinder, single coil)
8000rpm = 16000 pulses/minute (4 cylinder, single coil)
8000rpm = 8000 pulses/minute PER COIL (4 cylinder, 2 coils)
8000rpm = 8000 pulses/minute (2 cylinder, single coil)

Check my post again. I think we are saying about the same thing. The correction is due to the fact that the crank turns twice for each firing. (4 cycle)
 
Good point, I did double those numbers...

I thought you were saying that you could plug an auto tach into the neg terminal on one gs coil and get a correct reading with it on the 8 cyl mode? I was suggesting you would be 4x too high, which seems to be confirmed by that last post of meter results. I'm confused. 8O
 
gtsg01 said:
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.
Click to expand...
You get one pulse per revolution. Remember we are dealing with a 4 stroke. Each cylinder fires every 2 revolutions. Thanks for the measurements, this is what I was saying.

If an automibile has 8 cylinders and one coil it fires 8 times for every two revolutions of the crank. A 4 cylinder car fires the coil (single coil) 4 times for every 2 revolutions. The GS fires each coil 2 times for every 2 revolutions or 1/2 the count for a 4 cylinder tach wired to the coil. You then get 1/2 the RPM reading on the tach.
Click to expand...
 
fastpakr said:
Good point, I did double those numbers...

I thought you were saying that you could plug an auto tach into the neg terminal on one gs coil and get a correct reading with it on the 8 cyl mode? I was suggesting you would be 4x too high, which seems to be confirmed by that last post of meter results. I'm confused. 8O
Click to expand...
In an earlier post I did. I was using the Big N Dafts pickup coil data. His tach is reading 2x what it should. At the time I assumed we were discussing his situation. I was probably wrong on that one also. A 4 cylinder car tach would probably work for him. It's a moot point, since I don't think he is using a car tach.

Too many tach and pickup coil combinations here! :wink:
 
I did a quick search for Tach Adapters. Autometer makes a model 9117 that splices into the positive wire and senses the current fluctuations and converts them to a tach output.

On our bikes, both coils are powered from the same wire (orange/white) so if you put the 9117 into the circuit before the splice, the adapter would sense both coils, giving a combined 2 pulses per rpm.

http://www.egauges.com/pdf/AutoMeter/561.pdf

that would allow a readily available 4 cylinder tach to be used. The 9117 is listed between $68.00 and $78.00 on the web.
 
gtsg01 said:
I did a quick search for Tach Adapters. Autometer makes a model 9117 that splices into the positive wire and senses the current fluctuations and converts them to a tach output.

On our bikes, both coils are powered from the same wire (orange/white) so if you put the 9117 into the circuit before the splice, the adapter would sense both coils, giving a combined 2 pulses per rpm.

http://www.egauges.com/pdf/AutoMeter/561.pdf

that would allow a readily available 4 cylinder tach to be used. The 9117 is listed between $68.00 and $78.00 on the web.
Click to expand...
Glad to have you posting.

This is interesting. I've not seen this before. If it does what it says it should do the trick. The problem with using an auto tach is that they aren't weatherproof. Does anyone have a solution for that?
 
fastpakr said:
Ah, now it's all becoming much less mirky! Thanks for clarifying.
Click to expand...
I just looked back at the sequence of posts and I was wrong. Later on Big N Daft asked a question. This is all too confusing for me. :lol:
 
Swanny said:
fastpakr said:
Ah, now it's all becoming much less mirky! Thanks for clarifying.
Click to expand...
I just looked back at the sequence of posts and I was wrong. Later on Big N Daft asked a question. This is all too confusing for me. :lol:
Click to expand...

Thats why they call me Big N Daft!
 
gtsg01 said:
On our bikes, both coils are powered from the same wire (orange/white) so if you put the 9117 into the circuit before the splice, the adapter would sense both coils, giving a combined 2 pulses per rpm.
Click to expand...

correct me if I am wrong, but does the orange and white wire supply the 12volts B+, NOT the impulses? if so, how could this thingy 'sense' 2 coils?
 
propflux01 said:
gtsg01 said:
On our bikes, both coils are powered from the same wire (orange/white) so if you put the 9117 into the circuit before the splice, the adapter would sense both coils, giving a combined 2 pulses per rpm.
Click to expand...

correct me if I am wrong, but does the orange and white wire supply the 12volts B+, NOT the impulses? if so, how could this thingy 'sense' 2 coils?
Click to expand...
Yes, the orange and white wire is the battery.

It senses 2 coils by monitering the current in the wire. Notice that the way they have the coils wired in the example circuits. All of the coils are fed by one battery wire. The module is in series with it and can then detect any current fluctuations in ALL of the coils.

In order for this to work for you, you need the same configuration. You cannot have 2 separate wires delivering power to the coils since there is no way to monitor them both. Simply rewire the battery to the coils.
 
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