Blue Spark, but no combustion

cgguy09

cgguy09

1971 CB350 K3
Hey Road Warriors,

So this is a coil, condenser question. I'll begin with this: Compression is at 170 on Each cylinder, the valve gap is in-check (finally), point gap is good, brand new spark plugs, new coil wires, brand new coils, timed to a tee, brand new points, fully charged battery, full tank of gas, recent blood sacrifice to the gods.

I am getting no, or somewhat irratic, combustion on one cylinder. However, when I switch all the wires around the previously faulty cylinder runs perfect. Thus the problem is electric.

In examining the coils/plugs/wires....When I turn the bike over (electrically) I get what appears to be blue bright sparks on both plugs. I have both plugs sparking just as I pass "LF" or "F". I have switched the wires & the plugs (independent of each other) with no differentiating results.

So I am left with the coils or the condenser....

The coils are brand new. I mean BRAND new. I ordered them from DCC. That being said, of the two I originally purchased I returned one because it shorted out. The good folks at DCC sent a replacement no Q's asked. Now, the other one I originally got is the potential "problem." Could these coils just have been a bad batch? Seems odd? Could there be some gremlin on my bike that eats the inside of coils while I sleep?

I am also left thinking the condenser could be to blame. Is it possible the condenser would allow one coil to properly operate and the other to not? (I also recognize that the condenser is actually two condensers, so this seems wholly possible thanks to AlphaDog in a prior post http://www.dotheton.com/forum/index.php?topic=46811.0 )

I saw some witch craft test where you hook it up to a resistor and a battery...I am probably not going to do that. What I propose to do is isolate the condenser through just swapping the blue and yellow wires & keep everything else the same. Would this cause any potential problems? I'll avoid placing my logic for why it wouldn't. I would actually test it now, but it's 1100 & my neighbors would like to sleep.

Thanks guys, as always. Your advice, love, & attention are appreciated.

cFogs
BT
NNNN
 
cgguy09 said:
...I am getting no, or somewhat irratic, combustion on one cylinder. However, when I switch all the wires around the previously faulty cylinder runs perfect. Thus the problem is electric...
Click to expand...

You just answered your own question.

If swapping the coil causes the stumble to follow the coil, it's the coil. Also, you had one bad one; why not two? :)

-Deek
 
ILoveThumpers said:
You just answered your own question.

If swapping the coil causes the stumble to follow the coil, it's the coil. Also, you had one bad one; why not two? :)

-Deek
Click to expand...

I guess I just figured the odds of two bad coils was too great. Is there some setup in my system that would cause my coils to go bad? I am getting good voltage across the system, no apparent grounds.
 
Hey guys,
Still owe a picture of the points. I'll get that done today. I tested the condensor & that is good to go. So Deek is right, its the coil again.

I'm trying to figure out why I'm burning through these things. Are they just shotty products? Or could I be doing something else wrong.

I called DCC and I think they are helping me out. That being said. I have investigated the wiring and it looks solid. I have the Black & White Wire connected to the yellow wire and either the blue/yellow wire attached to the black. The coils are mounted to the original coil-mount via a fabricated aluminum stand.

When I go through the ignition timing process, I do notice the coils are particularly warm. Are the coils self-grounding? Because they should be grounded via the aluminum plate?.

Any ideas?
 
Stock coils need to be grounded, don't know about the DCC ones.

I've got a good pair of cb360 stock ones laying around if you want to use them for testing purposes.
 
Finnigan said:
Stock coils need to be grounded, don't know about the DCC ones.

I've got a good pair of cb360 stock ones laying around if you want to use them for testing purposes.
Click to expand...

I might want to steal those, or procure them through legal means.

I'm just trying to figure out how they woouldn't be grounded already. Maybe I should run some ground wires from the coil's two mounting screws to the frame to be safe?
 
Really don't have any knowledge about the aftermarket ones. If I can find them in my parts bin you can procure them
 
Three conditions will "ruin" a coil:

1) Excessive voltage. A coil for a 6v ignition system will not survive 12v for long.
2) Being continuously "on". You should not be sending voltage to the coils when the bike sits. This generates heat and the coil will eventually fail.
3) Excessive vibration. This one is less common, but cheap coils are not well secured in their cases and vibration will cause their leads (either the HT lead to the spark plug or the switching leads) to break internally.

You can test a coil by measuring the resistance of the primary and secondary windings and making sure they're in-spec.

Grounding: If a coil has only one terminal (+12v) then it grounds through the case and you don't want to paint the clamp, the clamp area or the clamp mounting point (you need a good path to ground). These will be zinc plated or galvanized. If the coil has two terminals, it will have a +12v lead and a ground lead. These are usually painted or sometimes they're plastic.

-Deek
 
ILoveThumpers said:
Three conditions will "ruin" a coil:

1) Excessive voltage. A coil for a 6v ignition system will not survive 12v for long.
2) Being continuously "on". You should not be sending voltage to the coils when the bike sits. This generates heat and the coil will eventually fail.
3) Excessive vibration. This one is less common, but cheap coils are not well secured in their cases and vibration will cause their leads (either the HT lead to the spark plug or the switching leads) to break internally.

You can test a coil by measuring the resistance of the primary and secondary windings and making sure they're in-spec.

Grounding: If a coil has only one terminal (+12v) then it grounds through the case and you don't want to paint the clamp, the clamp area or the clamp mounting point (you need a good path to ground). These will be zinc plated or galvanized. If the coil has two terminals, it will have a +12v lead and a ground lead. These are usually painted or sometimes they're plastic.

-Deek
Click to expand...

All good info,
These are 12v coils, so I am good.
I make sure they are not continuously on...I've made that mistake before (few years back).
The coils are pretty secure, they are not bouncing around at all.

So good on all those fronts.

The coil is plastic and has 2 (regular) wires leading from it (you can see it in the picture). You can see the mounting work I've done. Nothing to write home about, but it gets the job done. I simply attached a piece of cut aluminum to the stock mount.

Again, I checked the wiring & it seems good.

Thanks guys
 

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Finnigan said:
Stock coils need to be grounded, don't know about the DCC ones.

I've got a good pair of cb360 stock ones laying around if you want to use them for testing purposes.
Click to expand...

Stock coils are not grounded. They have 3 electrical connections. 12V (black Wire), wire to points (blue or yellow), and the High voltage spark plug wire.

Here's a excerpt from the Honda Factory Manual.

7p4n.jpg



You can see the 12V from the ignition switch is common to both the primary and secondary side. The primary then grounds through the points. The Secondary (high voltage) grounds across the spark plug. Since there needs to be a return path the the coil, the condenser acts as the completion of the secondary circuit. The properties of a condenser means it acts like a solid wire for a short impulse of current. That's why a bad condenser gives you a misfire, as the high voltage doesn't have a complete circuit.

Very few coils are externally grounded.

Here's a typical automotive coil cut away, where you can see none of the wiring is grounded. The (-) side goes to the points, the (+) side to 12V ignition, and the center to the plug wire. No ground.
qahq.jpg
 
Are you sure the coils are grounded? The metal core is not electrically continuous with the primary or secondary wiring. the Condenser is grounded and mounted on the same bracket, so they are grounded. The coils will spark and work hanging in free air though.

If you have grounded coils, then you have the only ones. Honda schematics for the CB350, 360, 450, and all point type induction coils are not grounded.

I have 2 sets of OEM coils, both of which I tested. One of the test is to see if any of the three electrical connections ( + , - , Spark Plug) are continuous to the mounting bracket. that's a fail.

I am not an electrical engineer either, but that doesn't change the manuals for these and other coils.
 
No, the condenser is mounted on the coil bracket and it needs to be grounded. The coils themselves do not. The metal mounting also acts as a heat sink. The coil itself is not grounded


Sent from planet Earth using mysterious electronic devices and Tapatalk
 
mydlyfkryzis said:
Stock coils are not grounded. They have 3 electrical connections. 12V (black Wire), wire to points (blue or yellow), and the High voltage spark plug wire.
Click to expand...

All coils are grounded. Whether its through the points or the frame, there has to be a path to ground.

-Deek
 
The blue and yellow wires ground through the points. It's the breaking of that ground that causes the spark.
 
ILoveThumpers said:
All coils are grounded. Whether its through the points and condenser or the frame, there has to be a path to ground.

-Deek
Click to expand...

The coils are NOT grounded at the mounting points. The case is not grounded. The Primary side is grounded when the points close. The secondary side grounds through the condenser.

The coils will work, with no physical external ground, with the points, 12V feed and sparkplug wire connected and the condenser grounded on one side, hooked to points side of the coil. The metal core of the coil is not a ground. It needs a metallic connection for heat sink, but not spark.

The discussion became about an external ground for the coils, not the points path or condenser path.
 
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