Tach adapter question

[AgentX]

OK, just checking myself here...

This tach adapter is meant to adapt a tach for a stock Harley to an aftermarket single-fire ignition. My assumption is therefore, that it doubles the signal input fed into it.

https://baronscustom.com/catalog/display/243/index.html


I currently have a tach which needs 2 pulses per rev (4-cyl car tach) but my bike (single-cyl wasted-spark) only gives 1 pulse per rev, showing half the actual engine revs.

Would this adapter work to make my tach read properly? (Guessing both coil leads go to my single coil, for my application...) Thanks!

 

[irk miller]

I don't see how it could. A tach designed for a single fire twin is reading two pulses per rev. The same goes for the four cylinder, which has two pistons working together. If your bike bike has a wasted spark, than that is dual fire. Harley cut costs running dual fire with a wasted spark at like 45 degrees or some shit.

 

[AgentX]

My bike is a single, so wasted spark gives one pulse per rev.

As you said, a single-fire twin is two pulses per rev. The tach for which this adapter is designed for a dual-fire twin, so four pulses per rev, correct? The adapter is designed for this conversion and so must double rev pulse input, yes?

That would be what I need, I believe. Of course there are a lot of variables I am not considering, in how exactly it doubles and times the pulses. And I freely admit I am inexperienced and speculating, which is why I am asking.

That said, I just ordered a different tach, so this is OBE anyhow...

 

[irk miller]

My bike is a single, so wasted spark gives one pulse per rev.

As you said, a single-fire twin is two pulses per rev. The tach for which this adapter is designed for a dual-fire twin, so four pulses per rev, correct? The adapter is designed for this conversion and so must double rev pulse input, yes?

That would be what I need, I believe. Of course there are a lot of variables I am not considering, in how exactly it doubles and times the pulses. And I freely admit I am inexperienced and speculating, which is why I am asking.

That said, I just ordered a different tach, so this is OBE anyhow...

Dual-fire still fires two pulses per rev, it just fires two plugs at the same time, such the term wasted spark. One piston is TDC, while the other is not.

 

[AgentX]

Dual-fire still fires two pulses per rev, it just fires two plugs at the same time, such the term wasted spark. One piston is TDC, while the other is not.

Ah, thanks. I wasn't sure how the vee-twin coils were set up, what kind of distribution was used, etc...hence the question. Much appreciated.