How to hook up a portable tach? - Motorcycle Forum
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post #1 of 5 (permalink) Old 04-27-2010, 05:41 PM Thread Starter
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How to hook up a portable tach?

Anybody know how to hook these things up?

I got my hands on an old one that is for 6 and 8 cylander engines(says just to multiply the reading from 8 cylinder setting by 2 to get 4 cylinder rpm), with tach, dwell, and pt. res... It's got a black wire, and a red wire, both with small alligator clamps on the ends..

I swear I've searched everywhere for instructions on how to hook these up(using wrong words/terminology?), and can't find it..
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post #2 of 5 (permalink) Old 04-27-2010, 10:40 PM
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You connect the black wire to a good ground; the engine fins will do. The other end connects to the wire from the points to the coil, usually at the coil. The other side of the coil is battery power, and you'll get no signal.

Rick
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'68-7? CB450 and '98 Valkyrie Tourer, too
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post #3 of 5 (permalink) Old 04-28-2010, 12:24 AM Thread Starter
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I've never worked with the coil before, so I really don't have much of a clue to where your saying to hook it up to. It seems I have one coil for each 2 spark plugs, so 2 coils on my bike? Which one do I hook up to?

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post #4 of 5 (permalink) Old 04-28-2010, 10:36 AM
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You can hook it up to either coil, the only issue is whether yours is a single-fire or dual-fire bike, that is, do both coils fire on every revolution, or only one? Firing only one per revolution is usually only on fuel-injected bikes, because the control system already knows which cycle the cylinder is on. Or, on bikes with points driven by the camshaft, like my old CB450.
If it fires on every revolution, the tach reading, when set to 8, will be multiplied by 4; otherwise, by 8.

Rick
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'68-7? CB450 and '98 Valkyrie Tourer, too
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post #5 of 5 (permalink) Old 04-28-2010, 05:16 PM Thread Starter
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Ok I got it, thanks.
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