Author Topic: Pulse Generator or Spark Advancer Issue?  (Read 618 times)

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Offline elcguapo

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Pulse Generator or Spark Advancer Issue?
« on: August 29, 2024, 02:10:22 PM »
Hi everyone. I have researched the subject extensively, but my 82 Nighthawk 650 has a unique issue where it loses spark alternatively at the 1-4 and 2-3 cylinder side, interchanging infrequently. I have tested the 12V feeds going to both ignition coils and they check out with power. I have swapped the two CDI box feeds which does not result in a change of the route (cylinder pair) of the issue, USUALLY. BUT, after swapping the CDI box route multiple times, on occasion the spark outage WILL move to the other set of cylinders. Though when immediately swapping back the lines the issue does not move back to the original side that was not firing. Would this indicate an issue further down the route at the pulse generator/spark advancer? In your estimation, can you think of a specific part that would be the issue? Many thanks in advance.
« Last Edit: September 05, 2024, 12:44:57 PM by elcguapo »

Offline beemerbum

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Re: Pulse Generator or Spark Advancer Issue?
« Reply #1 on: August 29, 2024, 03:55:40 PM »
It could be that SOHC enthusiasts are not familiar with motorcycles with "two CDI box feeds"

Offline HondaMan

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Re: Pulse Generator or Spark Advancer Issue?
« Reply #2 on: August 29, 2024, 05:30:58 PM »
Check very closely those little plugs where the modules plug into the bike's wire harness. The tiniest bit of corrosion on them, particularly the signal wire, will cause weak trigger signals to the module(s). It will be intermittent: sometimes they work better for a while after the bike is washed aggressively in a quarter-car-wash booth (guess how I discovered THAT one?). ;)

Cleaning the contacts in the female end of the plugs is hard to do. You can use a normal pencil eraser to clean the ones that you can see and touch. I ended up cycling them (unplug, plug back in) about 30 times to scrape the surfaces clean, then added a drop of LPS-1 to prevent it ever happening again. Don't be tempted to use WD-40 or any sort of lubricant for that: if you can't find LPS-1 then don't use anything on them.

I also located the grounds (there are, IIRC, 4 of them) on the bike and removed and cleaned each one, added a drop of oil and reassembled them. They carry significant current (unlike the spark modules) so almost any oil will work on those (even WD-40).
See SOHC4shop@gmail.com for info about the gadgets I make for these bikes.

The demons are repulsed when a man does good. Use that.
Blood is thicker than water, but motor oil is thicker yet...so, don't mess with my SOHC4, or I might have to hurt you.
Hondaman's creed: "Bikers are family. Treat them accordingly."

Link to Hondaman Ignition: http://forums.sohc4.net/index.php?topic=67543.0

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Offline elcguapo

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Re: Pulse Generator or Spark Advancer Issue?
« Reply #3 on: August 29, 2024, 07:38:22 PM »
Check very closely those little plugs where the modules plug into the bike's wire harness. The tiniest bit of corrosion on them, particularly the signal wire, will cause weak trigger signals to the module(s). It will be intermittent: sometimes they work better for a while after the bike is washed aggressively in a quarter-car-wash booth (guess how I discovered THAT one?). ;)

Cleaning the contacts in the female end of the plugs is hard to do. You can use a normal pencil eraser to clean the ones that you can see and touch. I ended up cycling them (unplug, plug back in) about 30 times to scrape the surfaces clean, then added a drop of LPS-1 to prevent it ever happening again. Don't be tempted to use WD-40 or any sort of lubricant for that: if you can't find LPS-1 then don't use anything on them.

I also located the grounds (there are, IIRC, 4 of them) on the bike and removed and cleaned each one, added a drop of oil and reassembled them. They carry significant current (unlike the spark modules) so almost any oil will work on those (even WD-40).

Thanks HondaMan. I did inspect the plugs of the CDI box connections with no detection of obvious corrosion. I was suspecting that there was a possible intermittent issue preceding the cdi boxes since the swapping of CDI box routes largely had no effect on which set of cylinders was not firing.

Offline scottly

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Re: Pulse Generator or Spark Advancer Issue?
« Reply #4 on: August 29, 2024, 07:52:54 PM »
The pulse generator coils should have a resistance of 500 ohms +/- 30 ohms, IIRC. (You might want to verify that.) Also, there is a specified gap between the bar on the inside and the protrusion on the advancer rotor, but I don't recall the number.
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Offline elcguapo

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Re: Pulse Generator or Spark Advancer Issue?
« Reply #5 on: August 29, 2024, 09:01:12 PM »
What leads me to believe that it may be an issue with the spark advancer is that - and correct me if I am wrong - it is the only component from the beginning of the ignition system chain that controls the two circuits leading to the cylinder groups, hence the alternating of intermittent failure of each cylinder. Thoughts?

Offline HondaMan

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Re: Pulse Generator or Spark Advancer Issue?
« Reply #6 on: August 30, 2024, 07:29:46 AM »
What leads me to believe that it may be an issue with the spark advancer is that - and correct me if I am wrong - it is the only component from the beginning of the ignition system chain that controls the two circuits leading to the cylinder groups, hence the alternating of intermittent failure of each cylinder. Thoughts?

The 650's spark advancer is largely 'fixed' in position due to Honda's attempts to meet the egregious DOT/EPA regulations contrived against Honda in the late 1970s. So, they don't provide adjustment: you only get to check it for malfunction.

That said: the spark advancer itself can (if messed with too much by someone) end up with some looseness in its operation that can cause erratic spark timing. The little lobe (they call it a 'cam') on the head of the advancer, which has the trigger 'bump' on it to fire the spark, has been found a bit loose from time to time from what I've read, though I wasn't there. So, check the advancer for things like too-soft springs (this will appear as reaching full advancer before 2250 RPM), which will cause erratic timing shift back-and-forth until higher RPM (like 3000+ RPM) when viewed under a timing light. If that happens then the springs may need to be trimmed back a little (start with 1/2 turn) to hold the advancer's weights steady. While you're there, make sure the advancer weights have not wallowed out their holes on their pivots: this makes for 'jumpy' timing when viewed with the strobe light, until the full advance is reached. Usually snugging up the springs will minimize this bug, too.

When the timing signal starts becoming too irregular the little CDI amplifiers cannot response fast enough to keep up with it, and they will not fire as the result. They have a built-in time constant that does the fast-charge fire of the coils, and it needs to be relatively regular versus RPM in order to work smoothly. If the timing marks jump around under a strobe light, this is the cause.
See SOHC4shop@gmail.com for info about the gadgets I make for these bikes.

The demons are repulsed when a man does good. Use that.
Blood is thicker than water, but motor oil is thicker yet...so, don't mess with my SOHC4, or I might have to hurt you.
Hondaman's creed: "Bikers are family. Treat them accordingly."

Link to Hondaman Ignition: http://forums.sohc4.net/index.php?topic=67543.0

Link to My CB750 Book: https://www.lulu.com/search?adult_audience_rating=00&page=1&pageSize=10&q=my+cb750+book

Link to website: www.SOHC4shop.com

Offline elcguapo

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Re: Pulse Generator or Spark Advancer Issue?
« Reply #7 on: August 30, 2024, 09:44:28 PM »
Thanks HondaMan. Really do appreciate the detailed response. A lot to unpack, but I plan on using this and your previous advice as a guide for my next diagnosis session.

Offline DaveBarbier

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Re: Pulse Generator or Spark Advancer Issue?
« Reply #8 on: August 30, 2024, 11:27:44 PM »
Hope you get this solved but two things.

The 650 doesn’t use a CDI system, it’s a transistorized system. So if you’re looking for diagnosing while searching for CDI it might lead you astray.

Lastly, if you happen to get fed up with the stock ignition (I hope not because when it works it’s totally fine) I made a post on getting a dyna s ignition to work on a 650. Check out my signature if you’re interested.

Offline elcguapo

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Re: Pulse Generator or Spark Advancer Issue?
« Reply #9 on: August 31, 2024, 08:13:05 AM »
Thanks Dave

Offline grcamna2

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Re: Pulse Generator or Spark Advancer Issue?
« Reply #10 on: August 31, 2024, 09:10:58 AM »
Hope you get this solved but two things.

The 650 doesn’t use a CDI system, it’s a transistorized system. So if you’re looking for diagnosing while searching for CDI it might lead you astray.

Lastly, if you happen to get fed up with the stock ignition (I hope not because when it works it’s totally fine) I made a post on getting a dyna s ignition to work on a 650. Check out my signature if you’re interested.

Dave,how's your 'Patina Hyena' running ?  Nice bike  ;)
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Offline DaveBarbier

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Re: Pulse Generator or Spark Advancer Issue?
« Reply #11 on: September 01, 2024, 12:12:27 AM »
Hope you get this solved but two things.

The 650 doesn’t use a CDI system, it’s a transistorized system. So if you’re looking for diagnosing while searching for CDI it might lead you astray.

Lastly, if you happen to get fed up with the stock ignition (I hope not because when it works it’s totally fine) I made a post on getting a dyna s ignition to work on a 650. Check out my signature if you’re interested.

Dave,how's your 'Patina Hyena' running ?  Nice bike  ;)
Running like a top, thanks Bill :)