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Discussion Starter #1
Hi, my "new" Vulcan 750 '98 has no ignition advance for rear cyl, front is ok. Any suggestion to solve this problem?. Top speed 70 mph.
 

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Discussion Starter #4
Yes, can test the ignition dinamic spark advance with a strobe lamp.Is totally controlled by the CDI unit.
 

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Don't really know, unless somehow the CDI isn't fully functional. Never had a timing light on mine. Some of us have been wondering about the start circuit wire running to the CDI, white/red or red/white, I've forgotten which.
 

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Hi Niko,
Among the regulars, nobody knows much about the specifics of the CDI box circuitry. It's been a mystery for some time.
Are there factory markings you are using with the strobe to check the timing? I'd be curious to see this on my own engine.
I know some people have used a file on the pickup coil mounts in order to change the ignition timing slightly, since modifying the CDI box isn't within the current knowledge pool.
 

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Discussion Starter #7
Red/White wire for the CDI unit comes from starter switch with + polarity. This signal to the CDI unit occurs only when the engine is in starting phase. I think that makes some kind of ease for starting the engine.
 

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Red/White wire for the CDI unit comes from starter switch with + polarity. This signal to the CDI unit occurs only when the engine is in starting phase. I think that makes some kind of ease for starting the engine.
That's what some of us figured, but have never found out for sure what happens with it. I intended to check it out but didn't get to it. It should be fairly simple, watch with a timing light during starts with the red/white connected/disconnected.

On a cold start, some added timing advance can help, but on a hot start less advance is desirable for easy starts.

As far as I know, you're the first to check advance between the two cylinders. Was it running poorly? Edit: I see now, "top speed 70". I would look at fuel delivery, ... slide diaphragms, carb vents, float height, etc.

Using a strobe, independent of ignition signal, would not be accurate. The light needs to 'see' when the spark occurs. That's why a timing light uses the coil wire to trigger the light. With the strobe, you're only seeing the timing mark when the strobe flashes, but not when the actual spark event occurs.
 

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Discussion Starter #9
With a timing light and the engine accelerating from 1000 to 4000 rpm, I can see that the top aluminum notch works smoothly from the blue to the green mark on the front cylinder. In the rear cyl I can see an erratic movement around the green mark.
 

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So you're using an actual timing light and not a strobe?

Did the factory provide marks to check both cylinders, or only one? The picture came out pretty small.
 

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Discussion Starter #12
Yes, a simple but modern xenon induction clamp timing light. There are timing marks for front and rear cylinders at the alternator rotor front periphery.
 

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Sometimes an erratic flash can be cured by moving the induction pickup to a different spot on the plug wire.
 

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Aside from the 70mph top end, is there anything else that drove you to think about looking into this timing thing? (Running rough, sputtering, lousy acceleration, flat spots during acceleration, etc.)

I would also ask if all of the other stuff on the bike are known to be good. (Hoses good and tight, no carb boot leaks, clean air filters, for that matter clean carbs, good oil/filter, good plugs, and so forth)
 

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Hi, my "new" Vulcan 750 '98 has no ignition advance for rear cyl, front is ok. Any suggestion to solve this problem?. Top speed 70 mph.
Hey Niko, I'm working on a replacement ignition controller on this thread.
I was able to set up the controller to plug right in and run with stock timing, fairly quickly.
I couldn't tell you anything about fixing the stock controller, but you can pick one of these up for <$200 shipped.
Quite a bit cheaper than a new OEM controller!
However, I suspect a broken wire in the pickup coil.

For everyone else following this thread, I ran a timing light on my bike with the OEM controller before I started my experiments.
What I saw was the timing marks are scribed at 0, 5 and 25 degrees for both cylinders.
At 1100, the light flashed at the 5 degree mark and smoothly went up to 25 degrees as RPM rose to 3500.
This was true for both the front and rear cylinders.

He should not be seeing with the erratic movement that he's seeing.
I would suspect an intermittent connection on the rear cylinder pickup.
The OEM ignition controller starts charging the ignition coil as soon as the pickup "sees" the target (the target is under the pickup).
The end of the target is at 5 degrees, so the timing is actually calculated from the start of when the pickup "sees" the target, and it will spark before the end of the target at above idle speeds.
If there's an intermittent broken wire for the rear, the timing of the target start and end point will be all over the place.
Engine vibration will cause all sorts of issues with a loose wire!
 
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