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Old July 30th, 2018, 06:45 PM   #1
Jpc647
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Wire going to coil - What is it?

This wire going to the coil. What does it do? The coil tab (that the wire clips into) has power when the ignition is on. If this is unplugged, the coil isn't firing, right?

IMG-4026.jpg
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Old July 30th, 2018, 06:48 PM   #2
Ceeloo Yello
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Must be ground wire then.
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Old July 30th, 2018, 07:22 PM   #3
Jpc647
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Quote:
Originally Posted by Ceeloo Yello View Post
Must be ground wire then.
It was more of a, how does that pin have power with the key on, if it's not connected. And, that must mean that cylinder isn't firing.
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Old July 30th, 2018, 07:39 PM   #4
Ceeloo Yello
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My understanding is the CDI pulses the ground wire to make the coil fire.
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Old July 30th, 2018, 07:41 PM   #5
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So yes if not connected, no spark.
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Old July 30th, 2018, 07:53 PM   #6
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Not CDI-capacitator discharge ignition system which send high-voltage +positive signal to fire coil that's always grounded. This is semantic confusion, like using "Kleenex".

Rather, it is Inductive Ignition which has advantage of much longer spark duration to guarantee ignition and complete combustion. This works by having coil always supplied with +12v to charge it (red wire). Then ignition box grounds other side of coil to fire spark (black wire). If you connect 'noid light to these wires (or use oscilloscope), you can see the grounding pulses.

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Old July 30th, 2018, 07:58 PM   #7
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Quote:
Originally Posted by Jpc647 View Post
It was more of a, how does that pin have power with the key on, if it's not connected. And, that must mean that cylinder isn't firing.
That disconnected terminal has power because it's connected to one side of coil. Other side of coil is connected to +12v. Imagine replacing coil with piece of wire with 2 terminals, if you connect one end to +12v, other end would have +12v also right?

Since one side of coil is disconnected, no current flows, therefore no voltage-drop V=IR. Voltage is same on both sides of coil. Until disconnected side is grounded by ignition box. Then black wire drops to zero volts (see scope trace above).

Issue you want to track down is whether that coil is receiving grounding pulses. Oscilloscope is alway my first choice because it shows not only binary yes/no "yeah there's pulse alright" like 'noid light, but it also gives me quality of signal such as duration and completeness of grounding pulse. Which can help narrow down issues with shorted wiring or bad coil problem.

For now, just plug disconnected wire back into terminal and see if it runs smoothly on both cylinders.

If not test for spark: pull plug-wire, stick known-good plug into it, ground case of plug by laying on top of engine, then crsnk engine. Also do test on other cylinder as control.

Last futzed with by DannoXYZ; July 30th, 2018 at 10:05 PM.
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Old July 30th, 2018, 07:58 PM   #8
Jpc647
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Okay. Thanks guys. I may have taken the carb apart and cleaned it for no reason.... :/
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Old July 30th, 2018, 08:13 PM   #9
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ALWAYS good idea to completely disassemble carbs to clean!!!
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Old July 30th, 2018, 11:12 PM   #10
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True but almost everyone refers to it as the CDI.
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Old July 31st, 2018, 06:14 AM   #11
Jpc647
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Quote:
Originally Posted by DannoXYZ View Post
ALWAYS good idea to completely disassemble carbs to clean!!!
Sure. I've taken the float bowls off, and they are perfectly clean. There's not a spec of gunk in the bowl, and the floats look new. This carb isn't gunked up. I'm going to clean it a bit, without a total disassemble, and put it back on, make sure the coil it on, and give it a whirl. I'll throw new plugs in too.
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