Vaild Coil Test?

[Radioguylogs]

I am putting the "electrical-system-in-a-bag" back onto my project SF.

The PO said he could not get a spark and threw an hand grenade in the fuse box, then starting removing all the electrical parts in the system. Don't know what he was thinking (or not).

As I am putting everything back together, I am trying to test as much as I can, to find a reason why the PO had no spark.

I measured the resistance of the ignition coils, and found the primaries were both normal (1.4-1.6 Ohms). I found the secondaries were 36kOhm and 26kOhm through the plug resistors. I found the reason one was high was that the plug resistors were 8k and 12k instead of 5k. Hmmm..should still work, but a thought for future investigation.

Just be sure, I wanted to test the spark. I put the spark plugs for each coil in a bench vice to complete the secondary circuit and avoid frying the insulation on the secondary winding. Then I manually tapped 12V onto the primaries with a 10A/12V power supply. There is no spark using either coil.

I tried some known good plugs. No spark.

Shouldn't this test show a spark? If yes, then maybe the PO already ruined the insulation on the secondaries?

Your thoughts are appreciated.

[crazy steve]

You really need to check the coils with the plug caps removed. While 25k ohms is the total you want to see, if you don't have the right combination you still won't get spark. You want 15k ohms on the coil secondary, and 5k on each cap, give or take a few k ohms for each piece.

And you won't see a spark until you remove the 12v input; it's the on/off switching of the coil primary that produces the spark.

[Gallaecus]

your resistance readings seem to be in the ballpark.
I have always noticed a difference in readings for caps 2 and 3 vs 1 and 4.
check your ballast for proper resistance as well.
you can cut a quarter inch off the spark plug wires before screwing the caps back on, and if they ohm out like you say, then i would think the coils are good.
you may want to put the coils back on the bike and check the input voltage to the coils. you may have a bad TCI.

[Gallaecus]

Shouldn't this test show a spark? If yes, then maybe the PO already ruined the insulation on the secondaries?

Your thoughts are appreciated.

if the insulation on the secondaries was ruined, you would not get the correct ohm reading.

[Gallaecus]

also, I have been recently introduced to the concept that the spark travels to one plug.....through the engine...up through the second plug and returns to the coil.

plus what crazy Steve said, cuz he knows what he is talking about.

so bench checking for spark is probably not necessary when the coils ohm out correctly.

[Radioguylogs]

The real question

Thanks for all the input so far. Honestly, I understood all of that very well.

My real question is whether the coils might have the correct resistance, yet arc over instead of producing a spark. It's easy to image that damaged insulation might arc, but not show up in a reistance measurement.

From the communities' response so far, the concensus says, "no...we don't see that in our experience".

In that case, I should put everything back together and see what happens. I'm quite skeptical it will work.

Further input is welcome.

[bikerphil]

I just got rid of the tired 30+ year old stock coils on my 79F and replaced them with Dynatek 3Ω and new replaceable wires. The bike runs sooo much better in every RPM range now, just my 2¢.

[TopCatGr58]

Hey Mike,

As was just mentioned, you need the spark plugs put into BOTH plug cap ends of the testing coil, and then connect them together, zip tie or TAPE, whatever, just so long as the grounding parts/threads/cases are touching each other, this way the spark energy can travel like it's supposed to, from one wire, thru the plug(s) and back up thru the other wire to complete the coil spark circuit. If you're just putting 1 plug in and collapsing the coils energized field, you won't see a spark because it has no where to go once it reaches the plug...if the plug isn't grounded to a frame, and that the other wire end isn't also connected to the ground source!

Secondly, the plug caps resistances do seem a bit too high....like you said, 5k is what you would expect, not 10. The plug caps can be taken apart, they unscrew from the inside, and you can remove the internal resistor, and check it out with the ohmeter, and if after cleaning the resistor, if it still measures close to the 10k range, then you'll need to get new caps...unless you want to replace the resistor with a nice SPRING and have no resistor caps, and just use resistor plugs.

What Phil said, many folks have reported on low rpm stumbles and misses and such, and did lots of carb work, only to find that once they replaced the old worn WEAK (15 Kvolts) oem coils with nice quality aftermarket units, Accel, Dynatek, or even Honda VF1000, so you get ~30+Kvolts at full 12 volts primary power(removing the ballast resistors), then their engines ran much smoother, started much easier, etc.!

T.C.

[Rasputin]

My real question is whether the coils might have the correct resistance, yet arc over instead of producing a spark. It's easy to image that damaged insulation might arc, but not show up in a reistance measurement.

Yes!!! if one has damaged insulation on the spark plug wires it may arc! It will also show up as good during a test as there is no break in the wire but one in the insulation. I have seen one of my bikes do the arc to ground when riding at night.
Thing is these coils suck to fix and the easiest way to go around it is to change them to optional coils. Some think that buying used coils from a Honda or whatever else may fit to be a good idea. Personally I do not agree as I buy new so I have some faith in them. I also buy quality over being cheap as many who have gone the el cheapo route have had to re-do them later.
I usually go the Accel route and have been happy. I will say to check each coil before you install it too. I had one bad coil show up and I tested it before installation. The company was happy to send me new with no questions asked. Try that with el cheapo units from mikes or ebay.
The other thing is that if you check your resistance in your caps and it is out of the proper specs then by all means change them out. Caps are about 7 bucks from yammie and cheaper elsewhere.

[motoman]

The Honda VF coils ARE a good option in spite of some of the nay-sayers who actually don't know the durability of Honda coils. Over 45yrs. associated on two wheels, rarely if ever have I seen Honda coils short to ground internally.

The Honda VF500 coils that replaced my tired 3ohm stock coils(2.3/2.4ohms respectively) last month definitely showed my low rpm carb issues were electrical. Both 3ohm VF coils checked out at 3 and 3.1ohms and plugs no longer black from idle to 4K.

[Radioguylogs]

Hey Mike,

As was just mentioned, you need the spark plugs put into BOTH plug cap ends of the testing coil, and then connect them together, zip tie or TAPE, whatever, just so long as the grounding parts/threads/cases are touching each other, this way the spark energy can travel like it's supposed to, from one wire, thru the plug(s) and back up thru the other wire to complete the coil spark circuit. If you're just putting 1 plug in and collapsing the coils energized field, you won't see a spark because it has no where to go once it reaches the plug...if the plug isn't grounded to a frame, and that the other wire end isn't also connected to the ground source!

Secondly, the plug caps resistances do seem a bit too high....like you said, 5k is what you would expect, not 10. The plug caps can be taken apart, they unscrew from the inside, and you can remove the internal resistor, and check it out with the ohmeter, and if after cleaning the resistor, if it still measures close to the 10k range, then you'll need to get new caps...unless you want to replace the resistor with a nice SPRING and have no resistor caps, and just use resistor plugs.

What Phil said, many folks have reported on low rpm stumbles and misses and such, and did lots of carb work, only to find that once they replaced the old worn WEAK (15 Kvolts) oem coils with nice quality aftermarket units, Accel, Dynatek, or even Honda VF1000, so you get ~30+Kvolts at full 12 volts primary power(removing the ballast resistors), then their engines ran much smoother, started much easier, etc.!

T.C.

Thanks for your thoughts T.C.

As I explained in the first post, I put the plugs in a bench vice to complete the circuit. The service manual (and Mike's XS) warn against firing the coil without the completed ciruit, warning that the winding insulation might be compromised by arcing.

I know from my days selling ign coils to automotive companies, that the secondary winding is usually about 40 gauge wire and looks like hair, not wire. It is rather fragile.

I did try to remove the 'unusual' resistors from the plug caps, knowing there was supoosed be a way. I tried from the spark plug side, not the wire side. There was nothing to grab onto, so I tried using pushing a small screwdriver against the ID of the metal collar. It didn't turn easily, so I was arfraid to try harder. Is there a trick? Or is the resistor on the wire side of the cap?

[Radioguylogs]

Maybe another insight

The Honda VF coils ARE a good option in spite of some of the nay-sayers who actually don't know the durability of Honda coils. Over 45yrs. associated on two wheels, rarely if ever have I seen Honda coils short to ground internally.

The Honda VF500 coils that replaced my tired 3ohm stock coils(2.3/2.4ohms respectively) last month definitely showed my low rpm carb issues were electrical. Both 3ohm VF coils checked out at 3 and 3.1ohms and plugs no longer black from idle to 4K.

The thought about rough idle and the remarks from Rasputin give me another insight.

One of my XS750s is hard to start under a particular circumstance.

If I have been riding awile, and I stop for gas, it will start easily. If I stop for 10 minutes, it is hard to to start. If I stop for 30 minutes or more, it is easy to start.

I am wondering if the heat from the engine after stopping might cause the coil temperature to peak about 10 minutes after stopping.

Just wondering aloud......

Anway, I will report my XSEleven findings when I get there.

Thanks again to everyone.

[skids]

If I have been riding awile, and I stop for gas, it will start easily. If I stop for 10 minutes, it is hard to to start. If I stop for 30 minutes or more, it is easy to start.

I am wondering if the heat from the engine after stopping might cause the coil temperature to peak about 10 minutes after stopping.

Thanks again to everyone.

This is common to all three of my xs11s. I find that if I pull out the "choke" lever, they will start. I suspect that the heat of the engine evaporates the fuel in the bowls and drops the levels (not sure). I suppose that switching to prime would also work, but I have never tried that...

[CaptonZap]

Thanks for your thoughts T.C.

I did try to remove the 'unusual' resistors from the plug caps, knowing there was supoosed be a way. I tried from the spark plug side, not the wire side. There was nothing to grab onto, so I tried using pushing a small screwdriver against the ID of the metal collar. It didn't turn easily, so I was arfraid to try harder. Is there a trick? Or is the resistor on the wire side of the cap?

If they are the NGK caps, you should get the resisters out of the plug end.
Look down in the cap with a strong light. You should see a round brass thing with a hole in the center down in the cap, and you should see a piece of wire cutting across a part of the center hole in the brass. (That is what ratchets onto the threaded end of the plug).
Now look at the shoulder surrounding the hole in the brass, and you should see two slots diametrically apposed to each other. A screwdriver slot with a hole in the center.
Use a sharp screwdriver, not one that someone used to scrape gum off the sidewalk with, and unscrew the brass thing. Lefty loosy, righty tighty.
Under it will be a small cylinder that looks like it is made out of cheap ceramic. That is the resister. It is about, from memory, and at 20 deg F out there, I am not going to go out and look, 1/2 an inch long and 3/16 inch diameter. I've seen some that were cracked in two, so check that. You can measure the resistance with an Ohm meter.

CZ

[TopCatGr58]

I thought I had already uploaded a copy of the exploded view of one of my caps to photobucket, but I had not, so that's why this is a little late! SO...here is a shot of one of the LONG OEM caps with the internal plug end screw out, the resistor, and the cap.

T.C.