Author Topic: Coil and cap test results  (Read 3711 times)

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Offline jakec

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Coil and cap test results
« on: March 11, 2022, 06:25:35 PM »
My bike ride as running bad after swapping on these free oil can type coils I got. It was running lukewarm on cylinder 1 and the idle was racing.

So I just tested everything and the results:

Caps (resistance):

10.6 (cylinder 1 which was not firing 100%)
11.75
4.7
No reading

Tested a brand new cap I have and it read 5.04

Testing coils:

12.63 battery
11.98 at black (brake light always on)
11.88 at blue (1&4 coil)
11.28 at yellow (2&3 coil)

I went and my old/original coils and they both measure exact same voltage as battery through the blue & yellow wires.

So from this I think I need all new caps. Would I need only one new oil can coil? They are $40 each. Otherwise if I need both I can go back to stock but this is for a chopper so they’re exposed and it’s not preferred.
1970 CB750 K0
1977 CB750 Chop
1984 Big Twin Evo Chop
1997 XR650L

Offline jakec

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Re: Coil and cap test results
« Reply #1 on: March 12, 2022, 09:35:59 AM »
I was hoping someone could tell me if the drop from 11.98 to 11.88 necessitates a new coil.
1970 CB750 K0
1977 CB750 Chop
1984 Big Twin Evo Chop
1997 XR650L

Offline bryanj

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Re: Coil and cap test results
« Reply #2 on: March 12, 2022, 10:02:26 AM »
You dont normally measure voltage but coil resistance
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Offline Don R

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Re: Coil and cap test results
« Reply #3 on: March 12, 2022, 11:06:37 AM »
 Check the primary and secondary coil resistance with them disconnected. Also remove the plug caps and check them individually.
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Offline xhevi

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Re: Coil and cap test results
« Reply #4 on: March 12, 2022, 01:09:19 PM »
I gave up on ngk caps for #2 and#3. Those kept going bad on me.

I use the same caps as #1 for all cylinders.

The longer stem caps (#1 and #4) seem to work out better for me.

Offline jakec

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Re: Coil and cap test results
« Reply #5 on: March 12, 2022, 11:28:10 PM »
I did my tests based on this post. So I have tested caps individually. I did not test coil resistance.

May I suggest that part of the problem is a general flail instead of a methodical troubleshoot approach?

Perhaps you'll try this?

1- Disconnect both the Yellow and Blue wire at the coil.

2- Check Black wire TO the coils with the key on.  Red probe on Black.  Black probe on a green wire or engine case where there is no paint.
If you don't have Battery potential (12V) or very close to it (do a compare to that at the battery terminals), the coils and ignition can't work.
Then fix the problem here.  Otherwise...

3- Reconnect the Black wires to the coils.  Now measure the disconnected Yellow and Blue wires each with the red meter probe and the Black probe on a green wire or engine case where there is no paint.
Again you should have Battery potential (12V) or very close to it.  If not, and you had voltage at the Black wire on the previous test, the coil(s) is bad.

4- Next lay #4 connected spark plug on the motor or wherever the spark plug body can touch a battery return path (engine, frame, Green wires, etc.)  With an extra wire, used as a temporary jumper, bridge the Blue wire to engine, frame, Green wires, etc.  Each time you remove the jumper, the spark plug should spark at the gap.

5- Next lay #3 connected spark plug on the motor or wherever the spark plug body can touch a battery return path (engine, frame, Green wires, etc.)  With an extra wire, used as a temporary jumper, bridge the Yellow wire to engine, frame, Green wires, etc.  Each time you remove the jumper, the spark plug should spark at the gap.

If you got the plugs to spark, you can rule out a coil problem and focus on a DYNA issue.  If not, there could be coil, lead, plug cap, or spark plug issues.

6 & 7- Assuming tests 4 and 5 were positive, reconnect the Yellow and Blue wires at the coil, and find out where these wires connect to the DYNA.  If you can disconnect there, repeat test 4 & 5 with the wires that would have connected to the Dyna.
If you still got plug sparking, most likely the DYNA or its attachement electrically to engine, frame, Green wires, etc. is compromised.  If not, you have an interconnect problem between Dyna and coils which you must track down and correct.

I still use points.  So, I can't help with the repair of a broken DYNA.

Cheers,
1970 CB750 K0
1977 CB750 Chop
1984 Big Twin Evo Chop
1997 XR650L

Offline TwoTired

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Re: Coil and cap test results
« Reply #6 on: March 13, 2022, 03:02:09 AM »
When the points close, it completes a circuit to draw current though the coil. As the coil has resistance, there is a voltage drop though the coil that is drawing current.  The SOHC4s should have only one point set closed at a time.  To measure voltage drop though coils, check for point closure for the coil you are measuring.  Probably have to rotate the crank to make the other coil show a v drop with points closed.  There are 5 ohm coil primaries and 3 ohm primarily rating for most coils intended for the SOHC4.  If you are measuring two different rated coils, then the v drop will be different between them.

Your open cap should be replaced.  The caps should have about 5k ohm resistance through them on most 750s.  Some of the original caps have 10k ohm, found on Canadian imports and CB550s.  I can’t find new 10 k cap anymore.  5k will work.  They just erode the electrodes a bit faster due to higher current flow.  The caps have a build tolerance of 10 % outside of rated spec.

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Lloyd... (SOHC4 #11 Original Mail List)
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Offline jakec

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Re: Coil and cap test results
« Reply #7 on: March 14, 2022, 10:34:14 AM »
I had read that the later bikes sometimes had 10k caps and think that could be possible for mine because the engine is from a 77 F model so the coils and caps probably were too. But for all 4 of those caps it was very hard to get a reading in the first place, whereas when testing with new caps I would get a reading right away. In any case I'm replacing all of them.

For the coil test are you saying that the coil that I had that tested low probably had points open, and if I test the other one with points open it would drop too? Meaning both are bad? And points open being the correct time to test them?

Thank you
1970 CB750 K0
1977 CB750 Chop
1984 Big Twin Evo Chop
1997 XR650L

Offline Bodi

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Re: Coil and cap test results
« Reply #8 on: March 14, 2022, 10:54:04 AM »
Voltage at coils doesn't mean much. They are most likely fine. The open #4 cap will cause problems with #1. Just replace the caps first, and see it all is good.

Offline jakec

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Re: Coil and cap test results
« Reply #9 on: March 14, 2022, 01:37:37 PM »
How can I / should I test the coils? How to test resistance?

I will try the old coils when my new caps arrive, before installing the original ones.
1970 CB750 K0
1977 CB750 Chop
1984 Big Twin Evo Chop
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Offline HondaMan

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Re: Coil and cap test results
« Reply #10 on: March 14, 2022, 07:26:35 PM »
How can I / should I test the coils? How to test resistance?

I will try the old coils when my new caps arrive, before installing the original ones.

Normal coils measure about 4.3-4.6 ohms across the primary side (that's Yellow-to-Black/white or Blue to black/white wire measurements). If they are some low-resistance aftermarket coils they might be closer to 3.0 ohms, or 5.0 ohms, depending on who made them. The secondary sides are harder to measure, but don't often go 'bad'. They can be anywhere from 1000 to 5000 ohms, depending on the coil.

The OEM plug caps were 7500 ohms on the 750 until the K5/F0 bikes, then they became 10k ohms after that. Today we can get 5000 (5K) and sometimes 10k ohm caps, most often the 5k must be employed. The main thing is: the plug caps on both wires of a given coil should match: if they differ by more than 10% total ohms then the one with the lower ohms will have a real weak spark.
See SOHC4shop.com for info about the gadgets I make for these bikes.

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Offline jakec

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Re: Coil and cap test results
« Reply #11 on: March 15, 2022, 08:27:28 PM »
I wonder which cap would have the lower ohm reading out of the 1&4 pair, with #1 @10.75 and #4 with no reading.

I just tested the resistance of both coils and they read 0.00? When the meter is on it will read “1  .  “

But when I hooked it to coils it changed to 0.00.

The reason I’m suspicious of these coils is because I didn’t have any problems before I switched to these from my stock Honda coils.
1970 CB750 K0
1977 CB750 Chop
1984 Big Twin Evo Chop
1997 XR650L

Offline HondaMan

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Re: Coil and cap test results
« Reply #12 on: March 16, 2022, 06:19:25 PM »
I wonder which cap would have the lower ohm reading out of the 1&4 pair, with #1 @10.75 and #4 with no reading.

I just tested the resistance of both coils and they read 0.00? When the meter is on it will read “1  .  “

But when I hooked it to coils it changed to 0.00.

The reason I’m suspicious of these coils is because I didn’t have any problems before I switched to these from my stock Honda coils.

Something you need to know: the coils these bikes came with new were 4.3 to 4.6 ohms resistance. There are MANY types of coils out there, and a lot of them do not directly interchange with these coils on these bikes. For example, if your new coils' primary resistance is 3 ohms, you will have a chronically low battery because of too much power being used by those coils, especially when the bike is ridden in city traffic with lots of idling. If you are running a Dyna S or Tytronics ignition then you must keep the engine above 3500 RPM just to 'break even' on power consumption.

I have seen other members here install coils from 1980s bikes, which are CDI-type coils that look identical and mount up the same, but are 2.4 ohms impedance. These can burn the alternator to a crisp if the wiring doesn't go first. I have repaired more than one of these bikes that suffered from that treatment.

So...if your ohmmeter does not have an ohms range marked "x1", then you will need a different meter to read the resistance of your coils. You can get a cheap one from Harbor Freight for about $7 (last time I looked) that has an x1, x10 and x1000 (aka 'x1k') range for resistance.
See SOHC4shop.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.
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Offline jakec

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Re: Coil and cap test results
« Reply #13 on: March 17, 2022, 11:21:39 AM »
This is my meter, does it have the correct setting? I was using the 20k setting. Is the weird symbol on the bottom right the 1x setting?

Are you saying the reading was 0.00 because I was on the wrong setting? because I was able to measure the cap resistance on the 20k setting which is in the same range (5ohm).

1970 CB750 K0
1977 CB750 Chop
1984 Big Twin Evo Chop
1997 XR650L

Offline bryanj

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Re: Coil and cap test results
« Reply #14 on: March 17, 2022, 01:42:50 PM »
Thats on 29 VOLT range not 20Kohm range
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Offline Bankerdanny

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Re: Coil and cap test results
« Reply #15 on: March 17, 2022, 02:37:27 PM »
Thats on 29 VOLT range not 20Kohm range

That is just a generic picture of the model the OP has, not him actually using it (note the person in the photo is measuring voltage on a 9V battery). He just wanted to know if he wsa using the correct scale.

Jake, I believe that 20K is the correct setting.
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Offline jakec

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Re: Coil and cap test results
« Reply #16 on: March 17, 2022, 02:45:19 PM »
That is just a generic picture of the model the OP has, not him actually using it

LOL!
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1977 CB750 Chop
1984 Big Twin Evo Chop
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Offline HondaMan

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Re: Coil and cap test results
« Reply #17 on: March 17, 2022, 04:38:54 PM »
Use the "200" ohm range. It will have a permanent offset of about 0.6 ohms added to any low ohm range readings - that's the nature of digital DVMs. So, if your coils are 4.4 ohms, it will read 5.0 ohms, or very close to that. Leave the leads connected for 4-5 seconds while the meter settles, as the low-ohms scales use a [cheap and cheesy] sampling A-D convertor chip that isn't real fast at low ohms ranges.
See SOHC4shop.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 My CB500/CB550 Book: https://www.lulu.com/search?sortBy=RELEVANCE&page=1&q=my+cb550+book&pageSize=10&adult_audience_rating=00
Link to website: https://sohc4shop.com/  (Note: no longer at www.SOHC4shop.com, moved off WWW. in 2024).

Offline jakec

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Re: Coil and cap test results
« Reply #18 on: March 18, 2022, 05:50:58 PM »
I just tested the oil can coils by the method you said above and they both read 3.8. so are you saying they would both be 3.2 in reality? and therefor maybe they are 3 ohm coils?
1970 CB750 K0
1977 CB750 Chop
1984 Big Twin Evo Chop
1997 XR650L

Offline Kelly E

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Re: Coil and cap test results
« Reply #19 on: March 18, 2022, 07:13:00 PM »
Use the "200" ohm range. It will have a permanent offset of about 0.6 ohms added to any low ohm range readings - that's the nature of digital DVMs. So, if your coils are 4.4 ohms, it will read 5.0 ohms, or very close to that. Leave the leads connected for 4-5 seconds while the meter settles, as the low-ohms scales use a [cheap and cheesy] sampling A-D convertor chip that isn't real fast at low ohms ranges.

Does that go for a quality DVM? I have a Fluke 16.
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Offline HondaMan

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Re: Coil and cap test results
« Reply #20 on: March 18, 2022, 07:17:51 PM »
I just tested the oil can coils by the method you said above and they both read 3.8. so are you saying they would both be 3.2 in reality? and therefor maybe they are 3 ohm coils?

Yep, that's about were most of the 3-ohm coils are. They measure 3.4 on my DVM, but 3.0 ohms on my analog mutimeter. I like analog meters much more, but they have become expensive and hard to find!
See SOHC4shop.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 My CB500/CB550 Book: https://www.lulu.com/search?sortBy=RELEVANCE&page=1&q=my+cb550+book&pageSize=10&adult_audience_rating=00
Link to website: https://sohc4shop.com/  (Note: no longer at www.SOHC4shop.com, moved off WWW. in 2024).

Offline HondaMan

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Re: Coil and cap test results
« Reply #21 on: March 18, 2022, 07:21:36 PM »
Use the "200" ohm range. It will have a permanent offset of about 0.6 ohms added to any low ohm range readings - that's the nature of digital DVMs. So, if your coils are 4.4 ohms, it will read 5.0 ohms, or very close to that. Leave the leads connected for 4-5 seconds while the meter settles, as the low-ohms scales use a [cheap and cheesy] sampling A-D convertor chip that isn't real fast at low ohms ranges.

Does that go for a quality DVM? I have a Fluke 16.

Yep.
The offset is due to the protection diode circuitry that is built into the A-D chips that are commonly used in DVMs. They have always been this way, ever since they went to battery-powered type units. There are some (like Keithley) plug-into-the-wall type DVMs that are better, but they start at about $750 for the basic version. Not many folks have them! I used them in automation machinery in my 'day job' for many decades, for taking ohms readings of the bridgewires in pyrotechnic trigger devices that the machines I helped build. You cannot test them with much current, lest they go off!

...and boy, are they loud when they do...!
See SOHC4shop.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 My CB500/CB550 Book: https://www.lulu.com/search?sortBy=RELEVANCE&page=1&q=my+cb550+book&pageSize=10&adult_audience_rating=00
Link to website: https://sohc4shop.com/  (Note: no longer at www.SOHC4shop.com, moved off WWW. in 2024).

Offline jakec

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Re: Coil and cap test results
« Reply #22 on: March 18, 2022, 11:20:06 PM »
What are the consequences of running the 3 ohm coils in my bike? I rode it two times.

Also what are they meant for? Harleys? Cars?
1970 CB750 K0
1977 CB750 Chop
1984 Big Twin Evo Chop
1997 XR650L

Offline jakec

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Re: Coil and cap test results
« Reply #23 on: July 14, 2022, 10:40:45 AM »
I'm working on another bike which is a Cl350. It has stock coils. I'm trying to test coil resistance but I get a reading of 0.00 on both coils. That's testing across B/W and yellow or blue colored wires.

I also tested the coils on a parts bike that I have which also has stock coils. The result was also 0.00. Just wondering what this means?
1970 CB750 K0
1977 CB750 Chop
1984 Big Twin Evo Chop
1997 XR650L

Offline rotortiller

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Re: Coil and cap test results
« Reply #24 on: July 14, 2022, 11:04:35 AM »
Quote
If you are running a Tytronics ignition then you must keep the engine above 3500 RPM just to 'break even' on power consumption.

From my experience I'd say someone needs to service their electrical system. The stock 750K7 in the picture has the lights on all the time as demonstrated in the test. I have had the Tytronics since 2017 and the alternator coming in rpm still holds true. I see Niche Cycle is carrying the full line now.  http://www.nichecycle.com/ncs/categories/electronics/ignition-system/electronic-ignition/tytronic.html