Topic: '72 500 Four 9.9 Volts No Spark

[Dr. Frankenstein]

I installed a new wiring harness into my '72 500 Four but have no spark. My battery is charged with 12 volts, but I'm only getting 9.9 volts across the points and 9.9 volts at the coil.

Coming FROM the coil, I originally had two yellow wires from each coil going into the black/white wires of the harness; the two white wires from the coils went into the blue and yellow wires in the harness - I cranked it, but no spark. (FWIW I think I had that set up wrong to begin with).

I switched the wires - now white wires going into the Black/White wire connector, and the two yellows going into the blue and yellow wires on the harness - cranked it, no spark.

The new coils look like the originals. They're the type with the primary wire molded into the body of the coil, with the white and yellow secondaries coming off of that. I have 3.5 ohms across the primaries, but nothing on the secondaries - one lead in the spark plug boot, the other touching either the yellow or white wire of the respective coil- maybe I'm doing it wrong? I should at least have one working - ?   

But with a fully charged battery, I should be getting 12 volts at the points, yes? The points are the original, but clean (I cleaned them and set the gap to .014). A test light lights up when the points cross the F mark on both points, so I know I have that set right...but 9.9 volts?  What am I not seeing here?


 

[Don R]

 We often see a big voltage drop across all of the old and corroded battery cables, bullet connectors and the ignition switch. Any load will use some current.
  It adds up especially on a headlight on bike. I'd think a 72 should have a headlight switch so the lights are probably not adding to the issue. A good battery will read over 12 Volts also.
 Remove the plug boots and check ohms between the high voltage cables. Then check the resistance of the boots, trim the wires a quarter inch and put them back on if all checks out.

[HondaMan]

Well, there's definitely too much voltage loss somewhere.
First, for the coils: test between the 2 pigtails for the 'primary' resistance (it will be less than 10 ohms) and between the 2 sparkplug wires for the 'secondary' resistance (it will be in thousands of ohms).

Then, get a battery charger and hook up to the battery and then turn OFF the handlebar RUN-OFF switch, then turn ON the key. Connect your meter's (-) probe to a bare spot on an engine case and to the battery Ground lug on the right rear of the engine: you should get 0.00 volts. If not, start by pulling out that bolt (and bracket) and cleaning it well, including removing paint from the engine's top right rear bolster (in case someone painted the engine, or this got corroded badly). This ensures you have a good ground to start: then go probing around with the meter's (-) lead clipped onto the ground lug.

[Dr. Frankenstein]

Hondaman - when I take that measurement with the battery charger, I get (interestingly enough) 6.5 mV at the ground bolt. Tested it again, and it went up to 8.5mV; tested it AGAIN, and it went up to 10 mV - and then, testing JUST from the Negative probe on the ground bolt and with the Positive probe to the front fender - 18mV !    I mean, "WTF??"

Measuring the coils, both primaries are 3.5 ohms, and the secondary resistance (between the plugs) is Plugs 1 and 4: 13.60 Kilo Ohms; plugs 2 and 3 is 24.2 kilo Ohms

I did paint the engine when I rebuilt it, so I'll take out the long engine bolt tomorrow, do some sanding and report back. But any ideas as to what may be going on, and what can I expect by sanding the engine mount?

[bryanj]

Expect less resistance in the ground path and no voltage drop battery neg to ground.
The electrons have to get round the system and back to the battery neg or nothing works

[HondaMan]

Yeah, like Brian says: the electrons are searching their way to ground,  and that causes something called "circulation current" where you'll be able to measure mV drops from any ground point to any other, and it will vary with temperature, pressure on the connections, and how happy your digital voltmeter's battery is (or not) at the moment! That's why the numbers will vary a bunch in the mV range, and why grounding solidly is real important. They also get lower at higher temepratures, and vice-versa.

Also, the white-ish powder in the little bullet connectors in the wire harness cold use some help today: the zinc plating molecules on them broke loose around 1986 or so and became pretty good insulators afterward. That's why you'll see me recommending a [painful] connector-by-connector cleaning-and-oiling process be done when waking up a long-stored bike (or even just over winter in some places). Higher humidity makes this worse: in deserts like Colorado or Arizona we get off a little lighter on this sentence.

Makes sure the clamp-and-mount system for the handlebars is likewise nice and clean, and I have sometimes improved the 500/550 electrics by adding a new, separate (green) ground wire from the e-panel on the bike's left side, alongside the wire harness, into the headlight (or the little triangle box under the tank on some of the later "F" bikes) to improve the overall grounding.

(On the early 750s this Green wire runs from that under-seat ground bolt to the headlight.)

[Dr. Frankenstein]

Got the bolt out, ground the paint off the frame, put the bolt back in - nothing.  I then switched the white and yellow wires coming off of the coils, just in case - nothing.  I changed out the old rectifier too, just because I had a new on one hand - nothing. The ground on the neck near the coils is clean and tight as well - nothing.  The only thing I can think of is the new (acid) battery I put in was only registering 12.10 volts, which seems kind of low given that I had it on the charger all night. I usually use AGM batteries on my bikes, but this one was new in the box and came with the bike when I got it; a bad battery, perhaps?? The acid in it came from a sealed container...

The only thing I still have to do is check the handlebar clamp, b/c I did repaint the dashboard, but could that really be it/ have an effect? I mean, does the whole frame act as a ground??

You mentioned ..."then go probing around with the meter's (-) lead clipped onto the ground lug." What exactly am I probing and looking for? The battery's Negative post and connection is clean and bright, as is the Positive post and connection, and it has new wires going to the solenoid...

The wires going to the plugs are new, and I even cut off a bit on each end and re-screwed in the plug caps...I am mystified as to what I'm missing here.

I'll put in some new points and condensers and see what happens, maybe it's those. Probably needs to be changed anyway.

[Ozzybud]

My bikes always have a lower voltage at the coils when they are plugged in as they draw a lot of juice.
Try unpluging  the black power leads to the coils and check the voltage now. It will be close to the 12v.
So the coils are causing the voltage drop.
I don't believe you have a  problem with that lower reading when plugged in.
The no spark is another issue.

[Dr. Frankenstein]

Nope - Nothing. I put in new points and condensers, the battery was at 13.3 volts - Nothing. I've been working on this thing since 11:00 am today, time to take a break and hit it again tomorrow, I guess. I am open to suggestions.

[newday777]

Nope - Nothing. I put in new points and condensers, the battery was at 13.3 volts - Nothing. I've been working on this thing since 11:00 am today, time to take a break and hit it again tomorrow, I guess. I am open to suggestions.

Aftermarket points and condensers?

[Ozzybud]

With the black wires energized you can ground the blue or yellow wire and when you pull it away from the ground it should spark. If it doesn't your coil is bad. It's what happens when the points open.

[Dr. Frankenstein]

I got the points and condensers from 4into1; the coils I believe I got on eBay.

Ozzy, I need some clarification on that method - what exactly do I need to do? The only black wires coming off the coil are the spark plug wires; the blue and yellow wires come from the coil and connect to the main wiring harness.  And I DO have 24.2 kOhms and 13.6 kOhms on the primary side of the coils, and 3.5 ohms on each secondary (cap-to-cap). 

Question: I've used dual-output 5 Ohm coils with great success on my Goldwing; can a '72 CB500 handle those, or is that too much?

I still think I'm missing something...(obviously I am...)...I have this nagging feeling that I'm missing something in the headlight bucket - what wires can I check that should be connected - what colors to what colors? Any obvious grounds?

[newday777]

"I got the points and condensers from 4into1"

Ditch them in the trash.
Do you have an old set from Honda with TEC on them?

[Dr. Frankenstein]

I still have the ones that came on the bike; I had them sparking before I decided to change them out to see if it made a difference (I don't throw anything away). Truth be told, I'm beginning to see the light about 4into1 and their shoddy products - they screwed me on some rings that allegedly fit the 500, but they did Not. I was lucky to be able to return them. I'm starting to use CruzinImage out of Japan when I go looking for parts these days. 

[newday777]

Get the complete points plate assembly. #1

Cheaper than individual points and condensers.

https://www.southsoundhonda.com/--xpartsstream#/Honda_Powersports/CB500K1A_MOTORCYCLE%2c_JPN%2c_VIN%23_CB500-2000001/POINTS_%2b_SPARK_ADVANCER/893400f5-1ca1-4586-9ff3-e8a62d9107fb/f5aa2f64-217e-49fb-b97c-96730455b630/y


https://www.southsoundhonda.com/--xpartsstream

[Ozzybud]

Each coil should have 3 leads coming out. The large high tension wire for the spark plug and one small blackand a yellow or blue. The small black is the power feed and the colored goes to the points or breakers to break the ground and cause the firing🔥.  See picture below
If there isn't another wire coming from the coil you are not powering your coils.  Where did you get the 9.9v reading? You should have been checking the (black) power feed.

[Ozzybud]

Correction.  The female bullet plugs for the coils are black with a white stripe.  I believe most stock cIils have the male side solid black or black white

[scottly]

I installed a new wiring harness into my '72 500 Four but have no spark. My battery is charged with 12 volts, but I'm only getting 9.9 volts across the points and 9.9 volts at the coil.

When the points are closed are you reading 0 volts, and 9.9 when the points open? How are you checking for spark?

[Dr. Frankenstein]

I check for spark by laying the plugs against the engine and cranking it. I'm planning to give a more thorough going-over tomorrow. I have a feeling it's something SO simple, yet elusive...

[scottly]

Are the spark plugs clean or new?

[Dr. Frankenstein]

New; D7EA's if I recall...but I've spent the afternoon going over everything, watching videos from Common Motor Collective (very informative, too), using a fully charged battery (13.3 volts) - and I just cannot figure out why I have no spark! However: I measured the old coils and got 4.2 0hms for the primary, but Nothing on the secondary - they were pretty crappy and old...these new coils I have measure 3.5 ohms Primary - might my coils be too cold??  I have no idea....    Start switch, maybe...? The ignition switch is new as well...

[Ozzybud]

You said in an earlier post that you did not have a black with white stripe or just black feeding power to your coils
Where were you measuring 9.9 volts? Did you ground and unground the blue or yellow wire simulating the points opening? As you do that it should spark. It's that simple. If it does not spark your coils are bad.
You can do this on the bench as well.

[Dr. Frankenstein]

I don't have any black or B/W wires; it's a brand-new set of aftermarket coils, with just white and yellow wires - and the spark wires, of course. See pic.  That 9.9 volts was across the points, but I changed them out for new ones and now don't have ANY voltage across the points! The coils are measuring 13.60 Ohms Primary on plugs 1 and 4, and 24.2 Ohms on plugs 2 and 3, and 3.5 Ohms on both Secondaries - - I have a fully charged battery (13+ volts) but it is just not getting to the coils or points for some reason. But WHY?? 

If the whole bike acts as a ground, does that mean the coil mounting bracket needs to be placed on bare metal? Does the dashboard need to be bare metal where it meets the handlebars?? Could it be a bad generator...? A safety switch?? The Start switch (which is OEM but cranks the bike just fine)??  I just Do Not Know...! I have continuity from all the wires in the rear to the bucket;

I'll try filing the points today and see what happens, but I'm doubtful...I still think it's because I'm not seeing something - electricity is not one of my finer points, either.  AS I mentioned, yesterday I noticed that the old coils measured 4.5 Ohms Primary - if the OEM coils are actually 5 Ohms, I'm thinkin' I'll get some of the dual-outlet 'make-your-own-wire' coils like I have on my Goldwings and go that route; the spark I got off of those practically left a shadow behind me!

[Ozzybud]

The coils do not need to be grounded.
The white wire should be energized from the battery.
Ensure that white wire has voltage from the battery. Take the yellow wire and hold it to a ground for a few seconds pulling away from the ground and the coil should fire.if it doesn't switch the yellow/white and try again. If there isno spark thr coils are bad

[Ozzybud]

There is a lot wrong in that picture above
Did the coils come with a diagram?
First the black with white stripe coming from your harness with a double female should be plugged into the white wires ,one from each coil. The blue and yellow coming from the harness should plug into the blue and yellow. One for 1,4 the other color for 2,3
You have one of the wires from each coil going to each other,the blue from one coil to the white on the other coil.