Condenser question

MarcD · Jul 7, 2022

Working on my ‘73 750 resurrection; got it to kick over and fire a few times on starter spray (still need to clean/rebuild the carbs) so looked at the ignition.

Blue spark at both plugs (removed and laying on the headbut not very robust. Cleaned/set point gap, replaced plugs/high tension leads, cleaned/Deoxit—ed all the primary wiring connectors (coils, condensers, ballast resistor) but still a fairly faint flame.

I’m thinking the half-century old condensers have gone to their reward, and have a new pair on order.

In the meantime, I was thinking of lashing up a pair of generic automobile condensers, but wonder about polarity.

Condensers are capacitors, and these are likely electrolytic caps, which are usually polarized. Given the positive ground wiring scheme, which way should a generic automobile condenser be clip-lead attached?

Or should I just chill out and wait for the new parts in the mail?

Thanks,
Marc

Derek Wilson · Jul 7, 2022

FWIW - Google says they are not polarity sensitive...

I personally have not used them for years - all my bikes have EI...

marshg246 · Jul 7, 2022

MarcD said:
Working on my ‘73 750 resurrection; got it to kick over and fire a few times on starter spray (still need to clean/rebuild the carbs) so looked at the ignition.

Blue spark at both plugs (removed and laying on the headbut not very robust. Cleaned/set point gap, replaced plugs/high tension leads, cleaned/Deoxit—ed all the primary wiring connectors (coils, condensers, ballast resistor) but still a fairly faint flame.

I’m thinking the half-century old condensers have gone to their reward, and have a new pair on order.

In the meantime, I was thinking of lashing up a pair of generic automobile condensers, but wonder about polarity.

Condensers are capacitors, and these are likely electrolytic caps, which are usually polarized. Given the positive ground wiring scheme, which way should a generic automobile condenser be clip-lead attached?

Or should I just chill out and wait for the new parts in the mail?

Thanks,
Marc

To see if the condensers have anything to do with your problem, remove them. Their primary job is to prevent sparking at the points. A little running without them won't hurt. If they fail open, the engine will run fine but the points won't last. If they fail closed there will be no spark. If they fail partly closed the spark will be diminished.

rweb · Jul 7, 2022

It's been my experience the bike will not run without condensers, it will spark and try but if it dose start it will run terrible. Automotive condensers will work, I used ones from a 60's Ford years ago. Ground the condenser body and attach the wire end to the points side of the coil.

robs ss · Jul 7, 2022

marshg246 said:
To see if the condensers have anything to do with your problem, remove them. Their primary job is to prevent sparking at the points. A little running without them won't hurt. If they fail open, the engine will run fine but the points won't last. If they fail closed there will be no spark. If they fail partly closed the spark will be diminished.

I disagree - they act as filters, removing the AC current through the points, AC current gives a much weaker spark, with that characteristic yellow/orange colour. Will spark in open atmosphere but not under compression.
I am somewhat colour-blind so find determining a true blue/purple colour difficult - hence I now use one of these to catagorically determine if the plug is sparking under compression. Has at least 2 other bonuses:
1. No need to remove spark plug(s)
2. Complies with makers' stipulation (eg: Trispark) not to operate system without full HT circuit connected. "earthing" spark plugs risks not complying with this.

Spark Plug Tester In Line Ignition System Detector Coil Test Tools Engine JQ | eBay

<li> Features: 1.This is a in-line ignition spark tester. 2.Tests for no spark condition. 3.Good quality,stable characteristics,high reliability. 4.Suitable for professional or home use. 5.Essential for trouble shooting all internal combusion engines. 6.This is a in-line ignition spark...

www.ebay.com.au

Cheers

marshg246 · Jul 8, 2022

robs ss said:
I disagree - they act as filters, removing the AC current through the points, AC current gives a much weaker spark, with that characteristic yellow/orange colour. Will spark in open atmosphere but not under compression.

When the points are closed, the condenser is shorted out and does nothing. In the first instant the points open, without a condenser, a spark will jump between the points - there is NO AC. Uncharged condensers are essentially a short until charged. So, no spark jumps the points gap as the current flows through the condenser. The condenser is charged before the points are fully open and are no longer doing anything. Condensers do slightly affect the points effective time to open and therefore ignition timing - but it is slight and completely unimportant in the test I suggested.

Since this is a question about condensers, it has nothing to do with electronic ignitions.

Capacitors, including condenses and or inductors can filter certain frequencies of AC or noise. If you test the charge time of a handful of Lucas or other condensers you'll find widely varying charge times and therefore widely varying frequencies they could filter is used as a filter.

BTW, if your points are getting the mountain and valley - your condenser is not doing its job. It's either an open circuit or the wrong capacitance for the job. Using a 6- 8-cylinder car condenser is wrong. The points open much more often and often much wider therefore require a difference capacitance.

robs ss · Jul 8, 2022

marshg246 said:
When the points are closed, the condenser is shorted out and does nothing. In the first instant the points open, without a condenser, a spark will jump between the points - there is NO AC. Uncharged condensers are essentially a short until charged. So, no spark jumps the points gap as the current flows through the condenser. The condenser is charged before the points are fully open and are no longer doing anything. Condensers do slightly affect the points effective time to open and therefore ignition timing - but it is slight and completely unimportant in the test I suggested.

Since this is a question about condensers, it has nothing to do with electronic ignitions.

Capacitors, including condenses and or inductors can filter certain frequencies of AC or noise. If you test the charge time of a handful of Lucas or other condensers you'll find widely varying charge times and therefore widely varying frequencies they could filter is used as a filter.

BTW, if your points are getting the mountain and valley - your condenser is not doing its job. It's either an open circuit or the wrong capacitance for the job. Using a 6- 8-cylinder car condenser is wrong. The points open much more often and often much wider therefore require a difference capacitance.

Then why did they ever include condensers/capacitors in the circuit?
They still exist in the EI systems of today - just in circuit boards.
If the possibility of leaving the capacitors/condensor from the circuit was a realistic solution - don't you think that would be a well known fix to the yellow/orange spark problem?
In the 60's - 70's why not just remove the condensor? Because it didn't work!!
My response in this thread is purely to discredit false "witchcraft" which may lead others into a dead end
Cheers

marshg246 · Jul 8, 2022

robs ss said:
Then why did they ever include condensers/capacitors in the circuit?
They still exist in the EI systems of today - just in circuit boards.
If the possibility of leaving the capacitors/condensor from the circuit was a realistic solution - don't you think that would be a well known fix to the yellow/orange spark problem?
In the 60's - 70's why not just remove the condensor? Because it didn't work!!
My response in this thread is purely to discredit false "witchcraft" which may lead others into a dead end
Cheers

I suggested a test. Long term your points will not last without condensers. Condensers across the 12 volt wiring to ground would stop some noise and in old AM radio cars there was usually one screwed to the back of the radio for that purpose. There are capacitors in circuit boards to filter power supply noise and for oter purposes like wave shaping. Most likely there is a capacitor in parallel with the output transistor for the same purpose as the condensers across points. Like many things in electronics, components are used for multiple purposes.

I have done the test recommended many times. Also, when I see one set of points building a mountain I know the condenser needs replacing.

My degree in Electonics and my 50+ years' experience are not witchcraft.

MarcD · Jul 8, 2022

Thanks for the input and lively discussion.

I’d always thought the condenser in a contact points ignition system served two functions: a ‘buffering’ effect to protect the points’ surfaces from arcing/pitting, and a kind of amplification of the signal to the primary side of coil as it discharges, increasing the intensity of the secondary coil’s discharge to the spark plug.

Having encountered the ability of a capacitor to store and release electricity in a guitar amplifier (granted, much higher voltages), I maintain a healthy respect for them. Also, worth noting that electrolytic caps have a finite life, in use or not.

Hoping for a Eurotrash delivery today with both the new condensers and Amal rebuild kits. Will report back on results!

marshg246 · Jul 8, 2022

MarcD said:
Thanks for the input and lively discussion.

I’d always thought the condenser in a contact points ignition system served two functions: a ‘buffering’ effect to protect the points’ surfaces from arcing/pitting, and a kind of amplification of the signal to the primary side of coil as it discharges, increasing the intensity of the secondary coil’s discharge to the spark plug.

Having encountered the ability of a capacitor to store and release electricity in a guitar amplifier (granted, much higher voltages), I maintain a healthy respect for them. Also, worth noting that electrolytic caps have a finite life, in use or not.

Hoping for a Eurotrash delivery today with both the new condensers and Amal rebuild kits. Will report back on results!

In a positive ground Norton system, the points ground one side of the coil(s) and the other side is -6 volts. The condensers are wired in parallel with the points. When the points open the coil ground, for an instant the coil charges the condenser to -6 volts at which point it the condenser longer flows current. Since the coil primary magnetic field needs to collapse to cause the secondary to produce high voltage, the condenser is hampering not helping that to happen, but the effect is so tiny and short lived that it is negligible.

You can do all sorts of things with capacitors and inductors in music, especially with guitars. Clipping, boosting, wave shaping, etc. The simple fuzztone from the 60s was a wave-shaped over driven pre-amp. A few resistors, capacitors, and transistors. The more modern versions add a few more resistors, capacitors, transistors, and a couple of potentiometers. The originals only had an on/off (in circuit/out of circuit). The capacitors use in music is nothing like those in a points ignition.

Triton Thrasher · Jul 8, 2022

Yes you can use any condenser made for points ignition.

rweb · Jul 8, 2022

I bought my first Norton, a 72 in 1973 for $500.00 because the owner had rewired it and couldn't get it started afterward. After kicking, checking compression, spark and carbs in my spare time, it doesn't take long to tire of kicking a Norton during the hot Ga. summertime. After a few days I started tracing the wiring and found the condensers had been left out and removed from the bike. I had several used condensers so I attached one to each coil to the point side of the coil, it started on the second kick and ran fine. Those used condensers were on the bike when I sold it a few years later.

As far as condensers hurting point life I don't think so because it won't run without them. What will reduce point life and overheat the coils is running a 12 volt system that requires a resistor in the system, 6 volt coils, without a resistor. I also found this out in my younger days from experience on another project.

marshg246 · Jul 8, 2022

rweb said:
I bought my first Norton, a 72 in 1973 for $500.00 because the owner had rewired it and couldn't get it started afterward. After kicking, checking compression, spark and carbs in my spare time, it doesn't take long to tire of kicking a Norton during the hot Ga. summertime. After a few days I started tracing the wiring and found the condensers had been left out and removed from the bike. I had several used condensers so I attached one to each coil to the point side of the coil, it started on the second kick and ran fine. Those used condensers were on the bike when I sold it a few years later.

As far as condensers hurting point life I don't think so because it won't run without them. What will reduce point life and overheat the coils is running a 12 volt system that requires a resistor in the system, 6 volt coils, without a resistor. I also found this out in my younger days from experience on another project.

Ok, believe what you want, but it would be nice if you read what I wrote before saying I'm wrong. I never said that condensers hurt points or points life - I said the opposite!

rweb · Jul 8, 2022

marshg246 said:
I suggested a test. Long term your points will not last without condensers. Condensers across the 12 volt wiring to ground would stop some noise and in old AM radio cars there was usually one screwed to the back of the radio for that purpose. There are capacitors in circuit boards to filter power supply noise and for oter purposes like wave shaping. Most likely there is a capacitor in parallel with the output transistor for the same purpose as the condensers across points. Like many things in electronics, components are used for multiple purposes.

I have done the test recommended many times. Also, when I see one set of points building a mountain I know the condenser needs replacing.

My degree in Electonics and my 50+ years' experience are not witchcraft.

marshg246 said:
Ok, believe what you want, but it would be nice if you read what I wrote before saying I'm wrong. I never said that condensers hurt points or points life - I said the opposite!

I did read the second sentence in your post #8 above and you stated that Long term your points will not last without condensers. All I'm saying is that it's been my experience that a points type ignition system will not run long term or at all without condensers.... Your results may vary, mine did not.

MarcD · Jul 8, 2022

Installed new condensers (thank you, Joe at Eurotrash for the outstanding service!), pulled the plugs/put them against the head and kicked it through a few times.

Nice, fat spark every time. Previously had been weak and intermittent.

Also received a pair of carb rebuild kits, so will complete that task, reassemble abd see if it starts.

Points on the bike look ok, but got a new set to install after the experiment is complete.

Interestingly, the old condensers measured 0.44uf on my Fluke 175 meter, while the new ones measure 0.22uf. I’ve seen worse drift, but capacitance isn’t everything.

MarcD · Jul 8, 2022

started second kick, oil return within less than a minute, no horrible sounds.
First time this bike has run in decades, and it’s truly gratifying.

Last bike I had with Amal carbueration was a Bultaco Metralla, and it had one Monobloc. Got some learnin’ to do.

And thank again for the spirited discussion and ideas. This is a formidable task, and it’s great to have a lively forum to learn from, and hopefully contribute to!

Cheers,
Marc

ashman · Jul 8, 2022

I remember from way back when I ran points my bike had a misfire for some time when first started all good and ran great but after it warmed up started to miss fire, changed plugs and check timing but still did it then decided to replace the condensers and to my amazement no more misfire, problem solved but that was way back in the 70s, 79 I mounted my first EI a Lucas unit, it failed within 12 months then went with a Boyar, the first Boyar didn't servive the great fire of 83, but the replacement Boyar lasted 32 years and was still going when replacing with the JH maggie, so in short condenser can fail and should be replace when changing points, even in the JH maggie the condenser is part of the tune up kit.

Ashley

Shelby-Right · Jul 9, 2022

I replaced a mallory condenser years back with a tune up on a big block FE428 Cobra, it lasted about two days and motor wouldn't go , i was lucky that i had all the old bits in the car swapped condenser out, it said made in Mexico , makes me wonder about all the replacement ones for classic bikes , most likely chinese .

MarcD · Jul 9, 2022

Tried to post a pic of the old and new condensers, but the required skill eluded me. By appearance, they appear to be metal case electrolytic capacitors.

No matter where they’re made, these capacitors have a finite life, either in service or on the shelf somewhere. They will dry out and fail, either go dead or short to ground.

I’d mentioned guitar amplifiers earlier; vintage tube amps used electrolytic capacitors, often multiple section cans, for power supply filtering. There’s a nearly obsessive fanaticism about keeping these amps as original as possible (sound familiar?), but most amp techs acknowledge that if the amp will be gigged, the old filter caps need to be replaced, or at least watched like a hawk.

There’s a huge demand for new old stock vacuum tubes and even salvaged carbon composition resistors/mustard Mullard coupling caps by guitarists, but N.O.S. E-caps are not a thing. You want the freshest Sprague Atoms or replica CE Mallory caps wired up to those precious Fender, Drake or Partridge transformers!

Got carried away there….in short, condensers are cheap, not infallible and replacing them doesn’t detract a bit from your bike’s originality.

One more thing to bear pushing home…

Cheers,
Marc

MarcD · Jul 9, 2022

Condenser question

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