Topic: Timing Light Woes

[Loudpipe]

Took delivery of chopstar's beautiful modded CB500, and the only things he left for me to do were to synch the carbs and set the timing.  I hooked my inductive advance timing light up to cylinder #1, but the light doesn't flash like it should.  The bike definitely isn't missing... I'd hear it if it was (and have put over 100 miles on it now... definitely no missing), but at 2500 rpm the light flashes like once every 10 seconds, at random intervals, no matter how many revs it's doing.  I accidentally had it hooked up to cylinder #4 for a minute, and it did the same thing at high revs, but flashed what seemed like normally at low rpm (i.e. idle.).  The light is new... I've used it once on a TR6 and I've got the settings right (double checked).  Are the plug wires (which are new) shielded so well that the inductive pickup won't detect the electricity flowing through to the plug?  Any other ideas?

[Bodi]

Mine only works with the pickup clamp on one way - did you try reversing that?

[Loudpipe]

No...  Hmmm, I'll definitely try it, but I can't understand how that would make it work.  Seems like it wouldn't make a difference, but I'll take your word for it.

[Donzon]

My timing light is the same.  Hard to get enough flashes to do the timing and certainly not regular.  My pickup clip has an arrow that points to the spark plug and sometimes it works that way and sometimes I have to reverse it to get it working at all.  I've heard this from others as well, seems to be a common problem with these bikes for some reason.

Don

[bryanj]

If this light is powered by 12v you need to use a seperate battery BUT conect the neg on the battery to a good engine/frame ground

[Deltarider]

The inductive clamp usually warns Do not drop on the one side and This side towards plug on the other. Be careful with that clamp and avoid any impact as the graphite part inside can break (crack) easily. Our ignitions are of the dual output type. Plug 1&4 fire simultaneously and so do 2&3. That implies that if the 'This side towards plug position' works fine on the #4 pluglead, it's position has to be turned around when used on the #1 lead. Important: make sure the beak of the clamp is well closed and that the plug lead is dry and well cleaned before you start. Greasy plug leads can make a lot of difference.

If this light is powered by 12v you need to use a seperate battery BUT conect the neg on the battery to a good engine/frame ground

This is also my experience, although I can't explain why.

Maybe one of you can explain an observation I had all those years I have used my timing light. When I set the timing and check for advance at let us say 3000 RPM, I notice that when I increase momentarily to a much higher RPM, the timing seems to retard a little bit, as if the strobe can't keep up. Do you have the same experience?

[Loudpipe]

So use a separate battery (ie not the one on the bike), ground the second battery to the bike, and make sure the inductive pickup is clean/facing the right way?  Seems like quite procedure just to set the timing.  Wish it would stop raining here so I could have a go.

[Gordon]

Try pulling the spark plug boot partially off of the plug, just enough so there's a small gap between the boot connector and the top of the spark plug.  I've used this method on various bikes and cars when I'm having trouble getting a good strobe pulse, and it almost always works.

[Markcb750]

Plug 1&4 fire simultaneously and so do 2&3. That implies that if the 'This side towards plug position' works fine on the #4 plug lead, it's position has to be turned around when used on the #1 lead.

Can anyone explain this?  My electrical experience tells me current flow is in the same direction for both plugs in this coil & dual plug set up.


Mark

[Steve F]

Mine only works with the pickup clamp on one way - did you try reversing that?

Mine's the same thing, it works better if I reverse the clamp on the plug wire.  It still isn't the best but useable.  Clamping on plug wire 1 OR 4 won't matter, I usually use #4 anyway since it's on the same side of the engine as the points.

[mystic_1]

Plug 1&4 fire simultaneously and so do 2&3. That implies that if the 'This side towards plug position' works fine on the #4 plug lead, it's position has to be turned around when used on the #1 lead.

Can anyone explain this?  My electrical experience tells me current flow is in the same direction for both plugs in this coil & dual plug set up.


Mark

The HV side of the ignition circuit goes from the secondary winding on the coil, down to one of the plugs, through the block to the other plug in the pair, then back up to the secondary wiring.  Each time the coil fires, current flows as described, so one plug is "in" and the other plug us "out", so to speak.


mystic_1

[OldSchool_IsCool]

I've had this problem too.  I noticed that my plug wires have a thick outer sleeve over the actual wire.  When I place the incuctive clamp over the wire where there is no sleeve, it works much better.

[Markcb750]

Plug 1&4 fire simultaneously and so do 2&3. That implies that if the 'This side towards plug position' works fine on the #4 plug lead, it's position has to be turned around when used on the #1 lead.

Can anyone explain this?  My electrical experience tells me current flow is in the same direction for both plugs in this coil & dual plug set up.


Mark

The HV side of the ignition circuit goes from the secondary winding on the coil, down to one of the plugs, through the block to the other plug in the pair, then back up to the secondary wiring.  Each time the coil fires, current flows as described, so one plug is "in" and the other plug us "out", so to speak.


mystic_1

The engine block is at the negative, or ground, potential, the coil(s) are at a very high, [a few tens of kilovolts minimum], positive potential.

 I still do not understand how a circuit is completed from the electrode on plug "a", across the gap to the ground potential , to the second plug, to the electrode and back to the coil.  I do not think that is possible.

When the points open the coil field collapses, inducing a high coil secondary voltage which discharges across the gap of the plug.   Each spark plug in the Honda design  conducts approximately 1/2 the current generated by the collapsing field in the coil secondary to ground.  ( the electrons actually flow from the ground potential to the coil).


I think the problem is inductive coupling to the plug wires which is effected by distance, not any reversal of current flow between the paired spark plugs.

[TwoTired]

Mystic's description is exactly right.

The coil needs no ground reference, and that is irrelevant for current flow.  (FYI, A coil's output work on an AC model, not a DC model.  The rules are quite different.)  The coil does need a circuit conductive path for current to flow.  The two spark plug leads on the coil attach to each end of a coiled wire inside the coil housing.  The ends of the wire must become connected in order for current to flow through it.  When the voltage rises enough for the arc to form at both spark plugs current flows in the output coil using the cylinder head as a conductive path between the two spark plugs.  Therefore, one lead has the opposite polarity of the other as far as current flow is concerned. 
Timing light triggers can be sensitive to, and differentiate between, sensing a positive pulse or a negative pulse.  The ignition spark pulse has both a rising edge and a falling edge, which does occur on both leads.  However, the rising edge on one lead is the beginning of the event with a more rapid transition than the falling edge.  On the other lead the falling edge is the more rapid transition, and the rising edge is the slower transition.  Further, one side has had a nice stable reference voltage before rising edge occurs, whereas, the other lead has a very short period of stability before the rising edge if signal, in fact, only the width of the spark pulse.
Timing light trigger designs vary between models and brands.  Although a trigger circuit can be designed to be insensitive to pulse polarity, there is usually a goal to minimize parts count and cost of the circuit.  This usually means it will work better/best for the most predominant pulsing system in the automotive world, which is a positive pulse model.


Cheers,

[Jay B]

 (FYI, A coil's output work on an AC model, not a DC model.  The rules are quite different.)

TT, I'm sure no electrical genious, but could you expound upon that? There's nothing AC in the ignitions on these bikes, so what gives? Not trying to doubt you, but I never heard of anything like that before.

[Jay B]

Dont know why my response got in whith TT's quote, but I'm sure my ineptitude with computers had something to do with that.

[mystic_1]

TT knows way more about this than I do, and can surely explain it better, but one thing to keep in mind is that no electrons pass from the primary windings into the secondary windings.  All that happens is that the motion of the electrons in the primary winding (and the resultant magnetic field) INDUCES MOTION in the electrons of the secondary winding.  Now, electrons will only flow if there's a complete circuit.  No circuit, no flow.  A circuit is, bu definition, a circular path.  If electrons are traveling out of the coil via one lead, they MUST be returning to the coil via the other lead, otherwise the coil would eventually run out of electrons! 

mystic_1

[TwoTired]

(FYI, A coil's output work on an AC model, not a DC model.  The rules are quite different.)

TT, I'm sure no electrical genious, but could you expound upon that? There's nothing AC in the ignitions on these bikes, so what gives? Not trying to doubt you, but I never heard of anything like that before.

In essence, the points (in operation) turn the DC from the battery into pulsed AC power going to the coils.  Positive voltage to the coils (points closed) charge the magnetic field, remove the voltage to the coils (points open) and the magnetic field collapses.  The coil's primary, transfers power to the output coil's secondary, in the same way a transformer transfers power, with changes to the magnetic lines of flux.  There aren't any DC transformers, because unless the magnetic field lines of flux are moving across the secondary windings, no voltage is induced in the secondary windings.

By the way, when the coils spark the plugs, the collapsing lines of flux also cross the primary windings, and induce a voltage there, as well.  (something like 200-400 V).  The power travels back toward the points and is damped by the condenser.  In this way, the wire between points and coil actually have A/C current on them.  But, even discounting the Back EMF from the coils to points, the fact that the power going to the coils is not a steady voltage, but changing, makes the electrical model AC instead of DC.

Lastly, and ignore this if it is too confusing, many assume ground or 0V is a reference point.  And, this eases understanding of DC power distribution.  Usually A/C training begins with a model where ground is a reference and voltage is labeled for a positive cycle followed by a negative cycle.  However later you learn that it is the peak to peak excursion that is important (actually RMS, but that is getting even more complicated), particularly in transformer operation.  The transformer doesn't care about a true ground reference, only the peak to peak excursions.  It would work the exact same way if driven with +12V and 0V excursion limits ( happens in the motorcycle as it would with  +6 to -6V excursion swings.

[750goes]

Hey TT and Mystic,

can you offer some simple explanantion why his timing light is not flashing sometimes - I think that was the question?....

flux, RMS, OV,  ac/dc - whoa there............... (a little bit of tongue in cheek)


dumb aussie here.....

[Deltarider]

Important: make sure the beak of the clamp is well closed and that the plug lead is dry and well cleaned before you start. Greasy plug leads can cause disturbances. And be careful with that clamp. Do not drop it!

[Markcb750]

I should have looked at the wiring schematic.

Thanks to all for the interesting descriptions but what I see is one plug attached to each end of the secondary coil. I believe I understand it better now.

Let me put this in simplified mechanical engineers language...

When the primary loop is closed by the points electrical energy "slowly" builds in the coils. When the points open this primary field "quickly" drops to zero inducing an energy spike in the secondary coils.(induction across coils is caused by changing electromagnetic fields, the faster this change occurs the greater the induced current will be,)  The voltage is determined by the ratio of turns between the primary and secondary coils, the current determined by the decay rate of the primary field.

This high voltage conducts current to ground across the spark plug gap, with an opposite polarity at each plug due to the connection at each end of the coil.

Condensers smooth spikes in the primary circuit which generate sparks across the points causing pitting & desegregation of the contact.  [I put a solid state system on my K6 to eliminate this. ]


Interesting.


I bought a timing light last week to double check my static timing settings, the induction attachment to the plug does not seem direction sensitive, must be a characteristic of other pickups that makes  some sensitive to this.

I did find it difficult to clip on 2&3, 1 &4 where fine.  Made me wish for my long gone Craftsman timing light that went inline with the plug.  I made a minor change with the light, one or two degrees retarded from the static setting. 

Still battling a poor idle!   

[KB02]

When I got my Dyan-S system on my F1, I bought a set of their wires to go with it. I could not get my timing light to work with those wires. I grabbed an old spark plug wire from my Dad's old Ford F250 and plugged that in just for timing purposes then switched back to the Dyna wires once I was done.

BUT, if you were getting some random flashes, then this probably isn't your problem.

How is going by the way? This thread was started back in July. Hope you've gotten it figured out by now.

[Gordon]

Hey TT and Mystic,

can you offer some simple explanantion why his timing light is not flashing sometimes - I think that was the question?....

That was the question back in July.  The thread has since been hi-jacked.

[Markcb750]

Did not mean to Hijack the thread, just reading to make sure the timing light readings I was taking where meaningful, and I got to better understand something.   

Mystic's description is exactly right.

The coil needs no ground reference, and that is irrelevant for current flow.  (FYI, A coil's output work on an AC model, not a DC model.  The rules are quite different.) 

Not sure about this TT, I think the rules are the same, just one involves changing potential...and the joys of advance math to analyze properly.


If the system does not connect to both sides of the battery in this design it will not create spark because the system will not keep the engine/spark plug & secondary coil at the required electrical potential relative to the charging voltage delivered to the primary coil.


Just saying I think "ground" is important.

[mystic_1]

Thought experiment:


Take a working CB750.  Remove plugs 1 and 4, then reconnect them to the spark plug wires.  Connect the bases of the two spark plugs with large wire.  Hold them in mid-air so that they're not touching the engine.  Turn on the bike and crank it over.

Do the plugs produce spark?

mystic_1