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Bartrim, Todd wrote:
Now for the interesting part. I borrowed an inductive test tach (SunTune - an analog dial with settings for 2 or 4 stroke) and clipped it on the plug wires... and still zero. I tried all settings on all 4 wires under various engine speeds, but still nothing. I'm pretty darn sure that I've got good spark, 'cause the engine sure is smooth and powerful :-). My timing light has the same type of inductive clip for the spark plug wires and it works fine. The clip is directional (little arrow points to the plug) and I ensured it was on correctly, but just to check I even reversed it, but no luck. I checked the operation of the test tach on my Jeep and it works fine. So this leads me to question whether the Tiny Tach will work either. I guess Rusty will answer this question soon. I've not yet received my programmable divider counter chip yet, but I sure hope it works. Currently on the AeroElectric list, the Tiny Tach is being discussed by others on a different application. As electric Bob is engaged in the discussion, maybe I'll throw this one at him.
Now if I can get this tach issue sorted out, I will call for my final inspection.
S. Todd Bartrim
Todd,
What kind of plug wires are you running there?
A little background. When the current runs down the wire to the spark plug it sends a magnetic field exploding out in all directions. When the current is cut off at the end of the spark, that magnetic field come crashing back in. If a wire is washed about inside this exploding and collapsing field, it will experience a flow of current. You're antennae is a piece of metal, and it will sometimes pick up on this field and you will call it 'noise'. Sometimes people get rid of the noise by surrounding the plug wire in a conductor that will absorb most of the fluctuating field's energy. This piece of metal is called a shield, and you can actually buy 'shielded plug wires'.
These inductive pickup tachs your working with have a coil, or even a Hall Effect transistor, in the clip. The coil is nothing but a piece of wire wrapped in many tight little circles. More turns makes it more sensitive to the magnetic field changes.
So, with this theory: Your timing light might be working because it's pickup is more sensitive. That could be because it has more wraps of wire in it's coil, or because it has a more expsensive transistor. Or it could have a Hall Effect transistory and the tach not. But it's all to say that you're not emitting enough noise for the tachs, even though there is enough for the timing light.
Try using an unshielded wire on one plug that you attach the tach to and see if you get any response. If the tach works on your car, try pulling one wire from there for just a few minutes as a cheap test.
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----Because I can----
http://www.ernest.isa-geek.org/
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