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Discussion Starter #1
Hi all! I've got a 2003 Shadow Spirit 750 that I bought (ab)used and I'm having an issue that I can't seem to solve. I've spent 3 days scouring the interwebs looking for help but, alas, cannot find anything seemingly useful.

My issue: I HAD no spark on my front cylinder. Replaced the plugs(fouled), wires(worn), and caps(broken/cracked) all around, and the front coil. I now have spark but, it's a crap yellow/orange and barely visible. Rear cylinder has a nice thick blue spark, which it's had since I got the bike.
What can cause this? The internet says to check my stator but, from looking at the wiring diagram, the stator doesn't seem to affect the ignition system for this bike, just the charging system. Guess I can check the resistance there. It's easy to get to.
Could the pulse generator be bad? Seems like that would affect both coils not just the one?
Any help is appreciated.
Thanks!
 

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1983 Honda vt750 Shadow
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The stater is the charging system . So no, it won't cause one cylinder to miss.
But just in case, as we have seem so many times even with new batteries, jump it with a non running car battery and that way you can do all the testing without the possibility of a low voltage issue running you in circles.
If you have only 1 pulse generator that can't be the cause. But the ignition unit has 2 sections and some have had one side burned out and killed the spark to one cylinder.
 

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Discussion Starter #5
The stater is the charging system . So no, it won't cause one cylinder to miss.
But just in case, as we have seem so many times even with new batteries, jump it with a non running car battery and that way you can do all the testing without the possibility of a low voltage issue running you in circles.
If you have only 1 pulse generator that can't be the cause. But the ignition unit has 2 sections and some have had one side burned out and killed the spark to one cylinder.
Swifty- I'll give the battery thing a shot and see what happens. I'm assuming this is a CDI issue, I want to eliminate everything else before I get another one and it seems like I'm pretty much there.
 

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try swapping the coils front to rear? verify the coil is good.

When it come to electrical,,, The rule I follow is: The quantity on hand or the age of a part has NO relation to whether or not the part in the machine is good or bad.
 

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How did you fix the problem with the broken cap? I asking because the original plug caps have resistors in them.
 

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Try swapping the CDI boxes as well. I must have forgotten about your original statement, but that’s the area you need to keep looking in. Everything else just says when to fire. It’s the CDI boxes and coils that provide and magnify the ‘big’ voltage for spark.
 

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1999 Shadow 750 ACE VT750CD3 Modified
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There is only one ICM/TCI box on those bikes, so any swapping gets expensive fast and I think that's why the original poster wants to eliminate everything else first.
 

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Discussion Starter #10
How did you fix the problem with the broken cap? I asking because the original plug caps have resistors in them.
I bought new caps. They're pretty cheap if you go to the NGK website.I think I got 4 for $16 shipped.
 

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Discussion Starter #11
After taking Swifty's advice and hooking up a car battery to do some more testing, I'm not getting peak voltage at the new coil. So, according to the shop manual, I need a new ICM. I ordered one and will update after the weekend.
 

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I hope you tried swapping front for rear coil before condemning the ICM. As Oldguy said in a different way, new parts may be new, but that is no guarantee they are good.

How much is a replacement ICM for your 750?
 

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You simply have no idea how many times a defective new part led me down the rabbit hole before I learned my lesson.
Swap the coils to verify they are good. Also verify proper resistance through your new plug wires and caps. And the "ground point" when checking for spark.

Also; Check/clean the connections at the ICM, and your ground point connections. could be oxidation on the pins. Coils should have constant 12v input with key on and the ICM provides a momentary ground to fire them when triggered by the pulse generator coil. The fact that there IS a spark on the front indicates everything is working except possibly the coil/new wires or the ground points being used to test.

Edit: I'd think it's a possibility, but a remote possibility, the internal connections in the ICM could be bad, causing a high resistance connection on the front cylinder ignition path,,,
 

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Discussion Starter #14
I have absolutely run down the rabbit hole of bad new parts before myself, especially electrical replacements. I don't know that I'm at that level of hair pulling yet, but it's close.
I didn't bother swapping out coils because there is absolutely no continuity on either end or through the one that I replaced. As far as I can tell, testing wise, the new coil is fine. I don't really know how I would test how much current is going through it to the plug. I suppose I could still swap them. That rear one's a PITA, but it'll only cost me some sweat, literally.
The ground point when doing my spark test is the head, not the cover, so I don't see an issue there. I'll double check my battery connections and that my frame grounds are tight though.
Didn't think about checking the resistance in the wires and caps. I bought 7mm copper core wire and 5K ohm caps, dunno why I would have checked that but, I will.
The ICM connection should be good, as far as the connector goes. I've unplugged and plugged that thing back in enough over the last week or so to know that. I've got some contact cleaner, I can shoot some into the connector. Can't hurt anything.

The best price I've seen for a brand spankin new ICM is $270 + shipping. I picked up a used one for $75. You know, just in case, lol. I'm also a cheap bastage. I probably should have shown a bit more patience.

I greatly appreciate all of the help and suggestions. Looks like I've got a little bit more homework to do, lol. Between this and July in Louisiana, I'm going nuts. I just wanna ride.
 

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Just for information, measure the resistance of the old coil primary and the new one. Usually they are in the 2 to 2.2 ohm range on most of these engines. I have been looking at aftermarket coils on and off and see many are 3 ohms. Probably won't cause a excess current problem since it would limit current more than a 2 ohm, but it may also lessen the spark output. Just a guess.
 

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I was reading or looking at video, don't remember which now, but it was about testing an ICM ( but NOT on a Shadow). This was being done NOT by swapping with a known good ICM, and not with sophisticated equipment, but by faking the signal from the pickup coil, aka pulse generator with a simple touch from a live probe.

I haven't tried this yet, but the gist was that by disconnecting the pickup coil and substituting an intermittent connection to 12V B+, one could get that particular ( car) ICM to trigger a spark. It was suggested that this was because all the pickup coil did was to generate a cyclical voltage change, and that the ICM didn't particularly care if this was sinusoidal or a pulse. All the ICM was doing was triggering on the high/low or low/high transition.

But it seems to me that ICMs with a single pickup must be doing something a bit more sophisticated to trigger the spark for the 2nd cylinder. I'd want to understand a bit more about how this 2nd pulse is generated, and at least know what voltage is on the pickup coil circuit, before I started poking around with jumpers or test lamps hoping to diagnose something.
 

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I don't think you should do that. The manual shows a test of the pulse gen as a .7 volts signal (maybe AC volts). So 12 volts may be a killer of the ICM.
 

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That is an interesting system. My old 1983 750 has 1 signal arm that spins around each revolution and signals 2 pulse generators. Like having 2 sets of points to fire the 2 cylinders.
But yours has a multi finger wheel that signals only 1 generator.
Possibly it picks up all the signal points and uses the first and last point, or something like that, for the 2 cylinders and it could also use the multi signal to set the timing advance -???
 

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1999 Shadow 750 ACE VT750CD3 Modified
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These ICM boxes are pretty smart and yes the pulse signal is tiny.
This style uses a Hall effect sensor setup and counts notches, the same timing ring is used for a number of different bikes and the ICM varies by bike to suit the application with changes of timing and crank spacing.
This example is from an Ignitech manual:
289178
 

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I don't think you should do that. The manual shows a test of the pulse gen as a .7 volts signal (maybe AC volts). So 12 volts may be a killer of the ICM.
Good to know, thanks. It says .7V minimum, and signal is almost certainly some shape of sinusoidal variation, but I wouldn't be at all surprised if the pulse generator was on a 5VDC leg. That's definitely something you'd want to know before fakeying a trigger pulse. The guy who was doing it, and I'm remembering now, it was a video, was supplying power from B+ via a test light probe, so that would drop the voltage at the ICM signal terminal quite a bit.
But yours has a multi finger wheel that signals only 1 generator.
Possibly it picks up all the signal points and uses the first and last point, or something like that, for the 2 cylinders and it could also use the multi signal to set the timing advance -???
Somewhere I got the idea that ONE tooth on the timing wheel is larger than the others, generates a bigger pulse, and thereby sets the base rotation, and then the ICM counts pulses from that point for the 2nd cylinder.
 
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