Topic: Will a weak spark cause a bike to fail to fire up?

[miketayc]

Can't seem to find a straight answer on this and maybe its obvious, but will a weak spark cause a bike to fail to fire up?

I'm also wondering if a bad battery is the likely/only cause for having a weak spark across all my spark plugs( some slightly weaker than others).

spark plugs are all new, D7EA. The caps seem to vary in resistance from ~10.0k -  ~11.75k ohms. I figured the battery is probably why the spark looks so weak.

I have already ordered a new battery (AGM scorpion, heard it's a pretty good one from here). Been meaning to get a new one because I have completely drained my current one on more than a few occasions, and have had to keep it on a trickle charge most nights to keep the bike running.

PS Bike stopped running after a carb rebuild, but I'm trying to rule out coincidental electrical issues.

[evinrude7]

yes a weak battery will keep the bike from firing. 

[eigenvector]

You didn't say what your bike was, but crummy connections to the coils is another place for problems.  I replaced my coil wires with splices - so I don't struggle with this anymore, but before that - it was 50/50 odds the spark cap would be connected solidly.

[TwoTired]

A weak battery will drop its voltage when using the starter motor.  And, low system voltage will deny the coils of energy. You'll certainly have weak spark, then.
The CB 550 ought to have 10k caps.  I think they can be up to 20% tolerance.  So technically your plug caps are within spec.  I don't know where you can buy replacement 10 k caps though.  You should look into each end of the cap and check for oxidation or signs of arcing.  That would be bad.  I had some plug caps where there was a slot that allowed you to unscrew the internal contact and access the resistor inside.  It was a little cylinder of carbon. I was able to clean and tighten the carbon cylinder in the chamber and restore full contact.
Maybe yours can be improved?
Anyway, if you have to replace with 5k caps, best to start using resistor spark plugs, too.

Cheers,

[scottly]

PS Bike stopped running after a carb rebuild, but I'm trying to rule out coincidental electrical issues.

Sounds like a carb problem, rather than an ignition/electrical problem.

[miketayc]

Thanks again everyone. And yes it's a 550.
battery voltage fresh of the tender:
~12.23v when off
~11.6v when key on and kill switch is set to run
~11.70v when key on and kill switch off

I feel like I should note that my wiring for my starter switch is weird. I forgot exactly but the shop had to rewire some things and now I require a higher amp fuse to run properly. I've been meaning to contact them and get exactly what they did written down, because my starter button only works some times (i think when the charge is absolutely full) otherwise I have to kickstart.

A weak battery will drop its voltage when using the starter motor.  And, low system voltage will deny the coils of energy. You'll certainly have weak spark, then.
The CB 550 ought to have 10k caps.  I think they can be up to 20% tolerance.  So technically your plug caps are within spec.  I don't know where you can buy replacement 10 k caps though.  You should look into each end of the cap and check for oxidation or signs of arcing.  That would be bad.  I had some plug caps where there was a slot that allowed you to unscrew the internal contact and access the resistor inside.  It was a little cylinder of carbon. I was able to clean and tighten the carbon cylinder in the chamber and restore full contact.
Maybe yours can be improved?
Anyway, if you have to replace with 5k caps, best to start using resistor spark plugs, too.

I'll have to further inspect the caps, didn't try taking it apart. One thing I noticed(and couldn't understand why),was that one of the caps kept shocking me when testing, which seemed like another sign that at least that one is no good.
I did get new 5k caps because they're kinda cheap and I was being shocked and stuff, but didn't realize i needed to switch up the plugs. Is there simple D7EA resistor type plug equivalent, or does it not work that way?

[TwoTired]

Yikes, you have a battery and or tender problem.  The tender should maintain it at 13 volts or higher.  After a two hour rest the battery should measure 12.6 to 12.8 v.

If iyours measures that low just turning on the bike.  It is going to be way low when the starter is engaged.
No surprise you interpret weak spark.

Ngk makes DR7EA.

You got work to do!

Cheers,

[Duke McDukiedook]

Definite battery or charger problem as guys have said before me. That might not be your only issue though.

[Bankerdanny]

Points or electronic ignition? EI can be very sensitive to battery voltage

[tlbranth]

I'm only going to comment on the Scorpion battery. I bought 2 of these for 2 different bikes. Both failed within a year and failed very suddenly. I've since reverted to only buying Yuasa AGM - only because they are OEM and seem to give me good service with long life.

[miketayc]

Battery came in. It's at ~13v. Spark is definitely better, but not as bright as it should be. But I tried it with those old 10ohm caps.  Still waiting on the new 5ohm caps and resistor plugs to come in.

You didn't say what your bike was, but crummy connections to the coils is another place for problems.  I replaced my coil wires with splices - so I don't struggle with this anymore, but before that - it was 50/50 odds the spark cap would be connected solidly.

I will search for this after this post, but how exactly did you test for bad connections like this?

I'm only going to comment on the Scorpion battery. I bought 2 of these for 2 different bikes. Both failed within a year and failed very suddenly. I've since reverted to only buying Yuasa AGM - only because they are OEM and seem to give me good service with long life.

Damn, well too late now. i hope you're wrong haha

[TwoTired]

Battery came in. It's at ~13v. Spark is definitely better, but not as bright as it should be. But I tried it with those old 10ohm caps.  Still waiting on the new 5ohm caps and resistor plugs to come in.

Bright spark might make you feel better.  But, that doesn't necessarily make for better combustion.  The 10K caps extend spark duration event by slowing the coil drain time, as well as extend spark plug life.   It has no effect on spark voltage.  That is the domain of the spark gap size and the atmosphere characteristics within the gap.

Maybe you will send me the 10K caps you don't want?  I have a hard time finding those for my 550s.  I'll pay for shipping, of course.

Cheers,

[Bankerdanny]

Take the resistors off of the plugs. The caps provide the resistance on SOHC/4's, not the plugs.

[TwoTired]

If you can only get 5k caps, then the only way to restore the 10k goal is to use resistor plugs as well.  The plugs have 5k resistors in them and the resistance is additive.

Cheers,

[Deltarider]

The 10K caps extend spark duration

That remains to be seen and if the difference is significant. I promised to ask the experts. I kept my promise and asked three parties. So far none has replied. I guess they're still studying it  .

[miketayc]

So I tried starting again with the new battery, no go. I wasn't expecting much though. But I decided to check on the points. And may have discovered some other issues. With the plate off I tried starting it up, and noticed consistent sparking. It was dark out so it was easy to see. I've read here some sparking is fine, but I'm not sure where the line is drawn between ok vs too much.

I don't know much about points yet, but they look fine. I don't notice any corrosion or anything. However, if my understanding is correct. As I rotate the 1/4 and 2/3 points should touch and separate by specific length. However, at no point do either points separate, they appear to be constantly stuck together? maybe I'm looking at it wrong, but if I'm not this seems very wrong to me. But I'm curious if anyone can tell me what would this scenario typically cause, what kind of issues should I expect? weak spark/starting issues?

I'm waiting on proper tools to adjust them properly(feeler gauges/circuit tester). But I tried to see what I could do with just a multimeter and a wrench. but it seemed very out of wack. I figured my multimeter should shoot up to ~12v when circuit is completed right? Well, I got readings no where near the 1/4 F mark. I loosened up the plate and tried adjusting, but couldn't find the sweet spot at all, ran out of room in both directions. But based on some readings, it doesn't make sense to do this until the gaps are properly set?

Also when I attempt to take voltage readings at the blue/yellow wires, I got readings at ~10.3v or maybe it was up to ~10.8v I forget. BUT the coils were definitely at 10.3v. Either way, a voltage drop of 2.2v seems like a lot. I was wondering if someone could confirm or deny that.

Maybe you will send me the 10K caps you don't want?  I have a hard time finding those for my 550s.  I'll pay for shipping, of course.

Yeah sure, once I get all this stuff sorted out. Once the 5k caps come in I'll have a redundant cap/plug set. I'd like to see which works better but I'll probably be going with the 5k set, because I think I ruined one of the caps. The plastics on one of them is broken. But I'd be happy to send them to all to you. No problem

[TwoTired]

The 10K caps extend spark duration

That remains to be seen and if the difference is significant. I promised to ask the experts. I kept my promise and asked three parties. So far none has replied. I guess they're still studying it  .

I suppose 40 years of combined education and experience in the electronics industry just isn't enough to qualify my analysis.
If you know enough, predictive behavior of electrical matters is forthright.  A bit like using known formulas to obtain an answer before making a measurement confirmation.

I'm sure you'll eventually find someone to offer counter opinion, whether valid or not.  I mean what's life without FUD?

[Jimray23]

Your points dont get a noticable gap at any time while turning the engine over?

--------------------------------------------------
Jim
1979 kz1000b ltd
    stage 3 cams
    pod air filters
    4-1 open exhaust(no muffler)
    full rewire
    dyna-s ignition
    dyna 3 ohm coils

[TwoTired]

I don't know much about points yet, but they look fine. I don't notice any corrosion or anything. However, if my understanding is correct. As I rotate the 1/4 and 2/3 points should touch and separate by specific length. However, at no point do either points separate, they appear to be constantly stuck together? maybe I'm looking at it wrong, but if I'm not this seems very wrong to me. But I'm curious if anyone can tell me what would this scenario typically cause, what kind of issues should I expect? weak spark/starting issues?

There should be an observable gap between the points.  About 0.016", when on the high point of the cam.  No or little gap will mess with energy storage in the coils.

I'm waiting on proper tools to adjust them properly(feeler gauges/circuit tester). But I tried to see what I could do with just a multimeter and a wrench. but it seemed very out of wack. I figured my multimeter should shoot up to ~12v when circuit is completed right? Well, I got readings no where near the 1/4 F mark. I loosened up the plate and tried adjusting, but couldn't find the sweet spot at all, ran out of room in both directions. But based on some readings, it doesn't make sense to do this until the gaps are properly set?

When the points make contact, there should be zero volts across them, when they are opened the points should have the same voltage as that provided to the input of the coil primary.
But, you need to set the gap before adjusting timing.

After you get the point gaps and then timing adjusted, I'll warn you that faulty condensers can make sparking worse.  But, then again so can having the point gaps too small, as the back EMF from the coils can be 300V or more and make the sparking more impressive.

Also when I attempt to take voltage readings at the blue/yellow wires, I got readings at ~10.3v or maybe it was up to ~10.8v I forget. BUT the coils were definitely at 10.3v. Either way, a voltage drop of 2.2v seems like a lot. I was wondering if someone could confirm or deny that.

Did you confirm that the coils were being provided 12V on the B/W wires?
Do check the voltage at the supply connector to the coils (B/W wires).  If that is 10 v -ish then you have a voltage distribution problem to track down.

[Deltarider]

I suppose 40 years of combined education and experience in the electronics industry just isn't enough to qualify my analysis.

Does 40 years of repairing fans and hairdryers count as well?

If you know enough, predictive behavior of electrical matters is forthright.

The analogy of the waterhose you gave the other day is, let's say questionable. We educate our students with the analogy of the oldfashioned WC (the reservoir over your head) and flush pipe to explain the I, R and U in a DC system. Not in a sparkplugsystem and neither have I seen this anywhere before. I really don't know what effect a resistor in an HTlead and/or plugcap has on spark duration and I dont hide that I don't know it. That's why (and because I have never read anything about this before in any automotive literature, let alone in the extensive info NGK provides, I turned to experts (3 parties). Professor Steiner has forwarded my question to a collegue, all the mecs of the Dutch ANWB are still on it and so are the editors of a magazine (AMT) for professionals in the automotive branch. Because I don't know and I'm curious. I am humble and I leave it to others to impress with whatever what.

A bit like using known formulas to obtain an answer before making a measurement confirmation.
I'm sure you'll eventually find someone to offer counter opinion, whether valid or not.  I mean what's life without FUD?

I find your reaction childish, I'm really sorry, your Highness, but I can't help it. You sometimes state things without proof and then concoct what I call 'candy for the brain', to make it all 'perfect'. It's llike what you did before about aircleaner elements that had to loose their effectiveness because Honda had it in a maintenance scedule. That's how your mind works maybe, not mine. The truth is that the impedance is not documented and you take your own bike(s) as a starting point and then generalise. I questioned this 10KΩ before, because I estimate a total of 20kΩ in one circuit is quite a lot and if I have read the CB550 Parts Lists well, the Canadians as a consequence would have had 2 x 15kΩ = 30kΩ. That's even more. But then you say it must have been a typo. See how it works with you? Look, it could well be that you in theory are right with that spark duration, but it can't hurt to ask others, can it, the more I have never ever read about it before. And even when the theory is right, will we ever notice an effect? These are very normal questions, don't you think? Sorry for this, but I have read more than enough wishfull thinking in this forum and I like to sweep clean every now and then to clearly see what we do know and what we don't know. Nothing more, nothing less. And if I ever float into the field of wishfull thinking, I sure hope somebody will confront me with it. Now let's wait and see if the laws of physics will be unleashed on me again. 

[miketayc]

So I just got all the tools necessary to adjust and was surprised at how easy it was. That is if I did it correctly, because it almost seemed too easy. So maybe someone can confirm. I set the gap at the largest point to be ~.016. Now in terms of adjustment I'm only worried about lining up the dash between T and F(on both points) and making sure the light is on and voltage there? I guess I'm skeptical just because I thought finding that sweet spot would be difficult, but it seems that light stays on and voltage is found there more often then not? For instance, I lined up the dashes, and the light turned on. And for testing purposes I moved the plate in either direction (all the way)just to see if the light would turn off, but it didn't. Is this normal? the light does eventually turn off if I spin the shaft and the gaps closes, but I just want to be sure.

Did you confirm that the coils were being provided 12V on the B/W wires?
Do check the voltage at the supply connector to the coils (B/W wires).  If that is 10 v -ish then you have a voltage distribution problem to track down.

yeah IIRC, then yes I tested the B/W wires and received similar readings to those at the points ~10.3 - ~10.8, so I guess I'll have to figure out what a voltage distribution problem means. Is there another way/place to test voltage of the coils? But I have yet to test the voltage after resetting the points and such. Should I expect different results

[TwoTired]

The F mark is the coil fire point.  The points are supposed to open at that point as you rotate the crank past the F mark.  Rotating the plate, adjusts that opening point.  But, the plate is not always precisely captivated by the engine mount bosses.  Some plates are made undersize in diameter.  It's not obvious because the point springs place pressure on the plate and hold it against one or two bosses and the pressure varies as the point cam rotates.  This happens when the three screws are loosened to allow the plate to move about.

If you have dismantled the mechanical advance, know that it can be assembled 180 degrees out of phase.  This may explain why you are not seeing the points open when you expect, and explain why the engine won't run.

The voltage distribution system are the components used to route power from the battery terminals to the coils.
From your description, 10 V measured on the B/W wires indicates a loss of 2V in distribution.  It should never be more than 0.5V and less is certainly desired.
Use a wire diagram to follow the path the voltage takes on its way to the coils.  Wire connectors, fuse clips, keyswitch contacts, and OFF-RUN-OFF switch are all suspects in the voltage loss.  You may notice that the voltage loss is greater when the headlight is is on.  This is because the current impacts the magnitude of voltage loss, as the reistance encountered is fixed.
Ohm's Law.  V= IxR   Vary the current, the voltage changes in response.

Cheers,

[miketayc]

New 5 ohm caps/ resistor plugs showed no spark. 10hm caps with regular plugs showed very barely distinguishable spark, less than before. Tested the coils again, and became frustrated as I couldn't even get a reading above 10 ohms, like ~8.5 - ~9.5 with a lot of fluctuations, it was hard to get a stable readings. I have done nothing this past week but keep the bike/battery on a tender, and readjusting the points. 

The voltage distribution system are the components used to route power from the battery terminals to the coils.
From your description, 10 V measured on the B/W wires indicates a loss of 2V in distribution.  It should never be more than 0.5V and less is certainly desired.
Use a wire diagram to follow the path the voltage takes on its way to the coils.  Wire connectors, fuse clips, keyswitch contacts, and OFF-RUN-OFF switch are all suspects in the voltage loss.  You may notice that the voltage loss is greater when the headlight is is on.  This is because the current impacts the magnitude of voltage loss, as the reistance encountered is fixed.
Ohm's Law.  V= IxR   Vary the current, the voltage changes in response.

So I think I follow what your saying. I should basically check before and after one of these points(Wire connectors, fuse clips, keyswitch, etc , and see which has the suspect voltage drop?  Does the fix generally require replacement? I'm already suspicious of my off run off switch because I've the work that was done on the bike last summer.

[TwoTired]

The coil primaries should be in the neighborhood of 5 ohms.  The secondaries, around 13k or 15K IIRC.
There is no happy reason the readings would jump around, unless you have a broken or intermittent connection somewhere in the test set up or internal to the part being tested.  Is the meter display stable if you simply touch the probe tips together?

Anyway, you should have two coils to compare against each other.  Isn't one of them working?  If that one is having jumpy readings, scrutinize your test apparatus.

Your voltage drop fix could be a simple cleaning of connections.  Or, a rebuild of the key switch or run switch.  Can't really detail a fix until the problem is found and isolated.

For troubleshooting with the circuit active, you can measure the volts across each suspect component in the pathway.  The meter will read the Vdrop encountered directly.  Most likely, something is going to read 1 or more volts.  But, it is possible to have ten items with a 0.2 volt loss each.  Inline losses are additive.

Please be careful reporting readings.  10 ohms is a significantly different report than 10,000 ohms  (10K).  Your meter should tell you the difference if it is an auto ranging type.  Otherwise, the function knob selection must also be read to give the display proper meaning.

Cheers,