Tach reads too high

[AGCB]

I have a tach that says "for 1 or 2 impulses per revolution". It is reading too high (pegged). On a 98 Force 50, what type of tach should I look for. Does this engine send a pulse on the tach wire (or some other type of signal) and if so, how many per revolution?

Thanks,
Aaron

 

[jerryjerry05]

Your stator I believe is a 12 pole tach.
On the tach itself there might be a black thingy on the back it's the adjustment for different motors.
Try turning it to different locations.

 

[AGCB]

So the tach signal is from the charge circuit (stator) and not the ignition unit?

 

[gm280]

I have a tach that says "for 1 or 2 impulses per revolution". It is reading too high (pegged). On a 98 Force 50, what type of tach should I look for. Does this engine send a pulse on the tach wire (or some other type of signal) and if so, how many per revolution?

Thanks,
Aaron

If your tach actually states I or 2 pulses, then it is not a newer version with a selector switch on the back. And the only way it will work is if you can wrap a wire around one of the spark plug leads and see if that reads properly. Possibly it can get enough pulse from that lead and the tach use it... JMHO!

 

[Jiggz]

What kind of tach are we talking about? Is it a magnetic type, pulse type or inductive type? Magnetic type uses a magnetic pick up to count the rpm. A pulse type uses pulses from an ac stator and converts it to rpm depending on the number of pulses or poles the stator has. And the inductive type takes inductive voltage from the spark plug wires and directly converts it into rpm. So which one do you have?

 

[AGCB]

I believe it's a pulse type. Says "for 1 or 2 impulses per revolution, mag or battery ignition". I used it because I had it, left over from a homebuilt aircraft project which used a Subaru engine. It has a small wire loop on the back which is supposed to be cut if 2 impulses instead of 1. If I know how many impulses the Force puts out, I can build a simple electronic circuit to convert from that many impulses to 1 or 2 to make it work. The tach is made by Westberg Manufacturing Inc.

So do we have a consensus on a 12 pole stator?

Thanks for your input. I'm learning every time I ask a question. This is a great forum.

Aaron

 

[gm280]

I believe it's a pulse type. Says "for 1 or 2 impulses per revolution, mag or battery ignition". I used it because I had it, left over from a homebuilt aircraft project which used a Subaru engine. It has a small wire loop on the back which is supposed to be cut if 2 impulses instead of 1. If I know how many impulses the Force puts out, I can build a simple electronic circuit to convert from that many impulses to 1 or 2 to make it work. The tach is made by Westberg Manufacturing Inc.

So do we have a consensus on a 12 pole stator?

Thanks for your input. I'm learning every time I ask a question. This is a great forum.

Aaron

AGCB, I can appreciate your wanting to built a circuit to covert the pulses. However, If it truly is a 1 or 2 pulse input tach, then try connecting to the spark coil primary and see if you can get it to read. Building a conversion circuit is time consuming and trial and error effort and may not be needed... JMHO!

 

[Jiggz]

So how does your "tach" gets its input signal? Does it has a wire where you can wrap around a spark plug wire? Or does it needs to be connected to a signal source like an alternator or stator? Or does it has a wire that picks up a magnetic signal attached to a flywheel? As for spark plug signal source, the Force engine is a 2-cycle engine thus only puts out one signal per spark plug per revolution. The conventional tachs used on these motors actually get its input signal from the stator or alternator. Depending on the model this could be a 20 or 12 poles stator or alternator and the tach has to match such input signal to accurately read rpm.

 

[gm280]

So how does your "tach" gets its input signal? Does it has a wire where you can wrap around a spark plug wire? Or does it needs to be connected to a signal source like an alternator or stator? Or does it has a wire that picks up a magnetic signal attached to a flywheel? As for spark plug signal source, the Force engine is a 2-cycle engine thus only puts out one signal per spark plug per revolution. The conventional tachs used on these motors actually get its input signal from the stator or alternator. Depending on the model this could be a 20 or 12 poles stator or alternator and the tach has to match such input signal to accurately read rpm.

It actually sounds like a typical old tach that connects to the primary side of the spark coil and each time it pulses it gets a pulse signal to the tach. So I'm thinking he doesn't need to do anything but connect it up to one of the spark plug coils on the primary side... JMHO!

 

[AGCB]

It actually sounds like a typical old tach that connects to the primary side of the spark coil and each time it pulses it gets a pulse signal to the tach. So I'm thinking he doesn't need to do anything but connect it up to one of the spark plug coils on the primary side... JMHO!

I believe that's right and I'll give it a try.
Thanks