Spark Color

Discussion in 'Performance Mods' started by jaguar, Jun 18, 2014.

  1. jaguar

    jaguar Well-Known Member

    The strength of the spark is revealed in the color. A red or yellow spark is weak and probably will not spark in the cylinder. A blue or white spark is strong and has enough voltage to fight across the spark plug gap even under pressure within the cylinder.
    Notice the color of the spark, it should be blue/purple in color.
    A weak yellow spark is not very good and in most ignition systems means trouble. A bright blue is your most desireable and is usually a sign of a healthy ignition system. The hottest is an ultraviolet .

  2. jaguar

    jaguar Well-Known Member

    How to check your spark

    Take the plug out
    connect it to the spark plug cap
    put your gloves on and hold the spark plugs threads against the cylinder head fins
    (best to do this with little light. best at night.)
    position the plug so that you will be able to see the spark
    push the bike while watching for spark
    observe the spark color

    You can increase spark plug gap to see the spark better. Just don't forget to return it to the normal .025" afterwards.
    (as a side note- spark gap has a slight affect on ignition timing. larger gaps cause a slight delay.)
  3. OCCStingray

    OCCStingray Member

    WOW, so let me get this straight what your saying is that the further the spark has to travel the gap the slower the spark will arc? In effect retarding the timing?
    Man that is deep.
  4. bmg50cal

    bmg50cal New Member

    Taking from one source that says the speed of lightning is 2,485 miles/sec, which is a tiny fraction of the speed of light at 186,000 miles/sec.

    Convert it to inches/sec and we get 157,480,315 inches/sec. Run that against a 0.025" gap and the time to cross the gap is 0.00000000015874 seconds.

    How about we reduce the spark speed even to 1,000 miles/sec (it's a slow tired spark on a Monday morning badly in need of coffee) which would convert to 63,360,000 inches/sec. It would cross a 0.025" at 0.0000000003945703 seconds, we could double the gap to 0.05" and it would take 0.0000000007891 seconds to cross the gap.

    Looking at these numbers, does one really think that a wider spark gap would have any real effect on timing? :rolleyes7:
  5. max350

    max350 Member

    Simple tool (Vitage Mobelec Spark Tester) to check how strong the spark is

    Attached Files:

  6. jaguar

    jaguar Well-Known Member

    I like that tool

    The delay has nothing to do with the speed of electron travel. The output voltage from the high voltage coil isn't instantaneous. It ramps up to the high voltage. So as the spark gap is increased it takes longer to spark because the time it takes to ramp up to spark voltage is longer. Whether or not the time delay is worthy of consideration in the practical world is unknown though. I doubt it makes much of a difference when comparing small spark plug gap differences.
  7. HeadSmess

    HeadSmess Well-Known Member

    so, please explain how i see a spark thats in the U.V range? without having my cornea removed? (old wwII trick, people that have had cataracts removed can see UV)

    following that link, im with the purple with green polka dots... :jester:

    my theory is...unless its an ancient points system... if i cant see a spark in daylight....something needs tweaking.

    length of wiring/resistance of cables will have more effect on timing than any spark gap.

    whats more important in CDI is some kind of resistance in the HT side of things.

    why? the gap is considered "open circuit", until the spark occurs. at this point the gap is considered "short circuited" allowing full current flow.

    now this seems irrelevant, except...CDI has an issue in that the spark, while very hot, powerful and clean, is also very very brief. so brief, it can cause issues with actually lighting the fuel mixture!

    some resistance in the circuit simply reduces the current flow, allowing the spark to stay "on" marginally longer.

    um. i have to quote jennings here again...wait while i go track it down again :)

    meh. more forum referencing. more people with no idea telling each other whats what :)
  8. HeadSmess

    HeadSmess Well-Known Member

    here we are, direct quote. (p.160)

    But the capacitor-discharge system's best
    feature is that it is tremendously fast, faster than even the conventional magneto:
    Something in the order of 50-100 microseconds are required for a single electrical pulse
    from a conventional battery-and-coil to reach sparking strength; a magneto requires 35-
    40 microseconds (which is just below the wet-fouling level of 45 microseconds); but a
    good capacitor-discharge system takes only a couple of microseconds in climbing to full
    voltage, which means that it is so far below the wet-fouling level that it may be
    considered virtually immune to that disorder. Moreover, its spark is delivered so rapidly
    that firing will occur even when the plug is very badly fouled with oil or anything else.
    The single disadvantage of the capacitor-discharge ignition system is that it can deliver
    this terrific spark so briefly that ignition of the air/fuel mixture in the combustion
    chamber does not follow. Magnetos, for instance, keep their sparks going for about 0.5-
    1.0 millisecond, while the capacitor-discharge system's spark may last less than a tenth of
    that time. It has become common practice to add a resistor in the circuit to prevent the
    capacitor from dumping too fast and delivering a too-brief spark to the plug, but there
    still are systems being made without this feature - which is to be regretted - as cold-start
    problems will occur even with everything else in order, including a fresh, clean plug. A
    too-brief spark is also, likely to be unable to fire the kind of rich mixtures needed by two-
    stroke racing engines.

    how come noone ever mentions that important aspect when hyping up their super duper aftermarket CDI unit?


    note that this resistance does NOT delay any thing. it simply extends the duration of the spark. while the voltage builds, as long as the gap remains "open", the potential across the resistor will be zero. only when a current flows, ie, the spark is occuring, will the resistor have a potential across it...

    you dont want resistors on the LT side of the cdi, as the coil produces its sudden voltage rise by allowing the capacitor to discharge through it with no restrictions. slow the discharge down, and the voltage produced will be much lower, as EMF is directly proportional to number of flux lines cut in a given time by a conductor... more lines cut in less time...more volts :)
  9. jaguar

    jaguar Well-Known Member

    thanks for the input HS.
    I think the person that I quoted meant to write "violet" instead of ultraviolet.
    "It has become common practice to add a resistor in the circuit to prevent the
    capacitor from dumping too fast and delivering a too-brief spark to the plug"
    HS what he is saying here is not about resistance in the high voltage wire or cap. The voltage duration of the high voltage coil output has nothing to do with resistance since its duration is an exact copy of the duration of the voltage spike applied to the primary side of that coil. Adding resistance only lessens the current, therefore making the spark less hot and less likely to disturb radio communications. The needed resistance to keep the charge capacitor in the CDI from dumping too fast has to be in the current loop of that part of the CDI circuit. Now that you have made me aware of this slight problem I will experiment with different resistances in that loop and see if I can get a power increase as a result of less misfires (which are common in 2 strokes).
  10. HeadSmess

    HeadSmess Well-Known Member

    oh yeah. i misread :) but i still think its better in the HT side. in fact, im going to go raid the mechanics bin and use some silicone lead, get rid of the 22KV neon sign cable that is, well, highly conductive :) (it seemed like a good idea five odd years ago ;))

    also....worth investigating multi sparks, or "ringing" cdi systems. more than one spark! if the first one fails, maybe the second one will get it :) instead of the cap simply discharging, it "rings" as cap and coil forms an LC circuit. really makes a noticeable difference on BIG cylinders. ie, audi twin spark (it is audi, isnt it? though they use a different system as CDI does have a cap failure issue, something not wanted in a car that should do a few hundred thousand with no issues...)

    also read into the jaycar/silcon chip cdi replacement, where the designer has used a diode in a certain place so some of the reflected energy is used to charge the cap back up slightly.

    cap discharges into a coil(with as little steel in the core as feasible so it saturates quickly, unlike points). magnetic field builds (very rapidly in CDI). creates voltage in secondary winding(standard transformer). pop, sparks. then the magnetic field collapses, just like in a points system. obviously CDI uses stored charge, points use stored magnetic field.(without enough dwell, there isnt enough magnetic field produced, weak spark) this back EMF is usually dumped to earth or neglected altogether... USE IT!!!!
  11. HeadSmess

    HeadSmess Well-Known Member

    maybe he meant ultra violeNt?

    disrupting air molecules like nothing else on earth :)

  12. Fabian

    Fabian Well-Known Member

    somehow generating a spark so powerful that it's capable of denaturing physics.
  13. jaguar

    jaguar Well-Known Member

    I think the cap recharge idea would be useful mostly for engines revving over 12K rpm since there is normally plenty of time for the stator coil to charge that cap. But I like the idea of not wasting energy.
  14. HeadSmess

    HeadSmess Well-Known Member

    happens approximately 100 times a second, worldwide. lightning :)

    now we delve into the realms of tesla again... and that weird one...quantum physics :)
  15. jaguar

    jaguar Well-Known Member

    check out the ignition overview at

    Overview of Ignition Technology

    The Stages of a Spark Discharge

    The ignition process is key to the operation of internal combustion engines. Four-cycle engines require external combustion, and this is accomplished by discharging electrical energy through a spark gap. Heat transfer and gas ionization (splitting apart of gas molecules) caused by the spark discharge initiate a flame kernel. The flame kernel then grows into a flame front that spreads through the combustion chamber. The stages of a spark discharge include breakdown, arc, and glow discharges.

    Break Down

    Most engines require nearly 12,000 volts to fire the spark gap. When this voltage level is reached, a very high current flows for several hundred nanoseconds, an almost inconceivably short period of time, as energy stored in the capacitance of the coil, secondary wiring, and spark plug is rapidly discharged. Because the break down phase is so short, it accounts for only a small percentage of the total ignition energy. To better put this into perspective, at 6,000 RPM the crankshaft rotates less than 1/100 of a degree in 200 nanoseconds!

    Arc Discharge
    The break down phase is followed by an arc discharge. An arc discharge requires a considerable current flowing in the gap, usually on the order of several hundred milliamps. During the arc phase, the voltage across the gap drops to about one hundred volts. An arc discharge is very visible and high levels of energy are transferred to the flame kernel near the center of the spark gap. The duration of the arc discharge for a conventional ignition is usually no more than a few microseconds. Again, to put this into perspective, at 6,000 RPM the crankshaft rotates through less than 1/10 of a degree in 2 microseconds!

    Glow Discharge
    A glow discharge is less intense and the sustaining voltage across the gap is higher. A neon light is a good example of a glow discharge. It looks nice, but it doesn't generate a lot of heat. Much of the energy in the glow discharge is lost heating the electrodes or ionized gas near the electrodes. Conventional ignition systems have a short arc phase (some microseconds) after the initial breakdown followed by a glow discharge that lasts 1-2 milliseconds. At 6000 RPM, the crankshaft rotates through 36 degrees in one millisecond.

    Capacitive Discharge

    Capacitive discharge (CD) ignition systems are widely used in automotive racing applications with high RPM requirements. A special high voltage power supply charges a capacitor to 450 volts or more. Energy is stored in the electrostatic field within the capacitor and is proportional to capacitance times the square of the applied voltage. An electronic switch discharges this stored energy into the coil primary. A high voltage pulse then appears across the secondary windings and fires the spark gap.

    Spark Plug Wires

    Three types of spark plug wires are commonly available: original equipment style carbon core suppression, low resistance spiral core, and solid core. Carbon core suppression wires cause some energy loss due to their high resistance (about 5,000 ohms/foot). Replacing carbon core suppression wires with low resistance spiral core wires only increases spark energy by about 10%. Contrary to any claims, you will not see a performance improvement by changing spark plug wires. On the other hand, carbon core wires can deteriorate over time and any wires more than a few years old are candidates for replacement. If you are going to install new spark plug wires, buy a set of low resistance spiral core wires. Most are less than 500 ohms/foot. At that point, almost no energy is lost in the wire. There are some new versions with very low resistance (50 ohms/foot), but the advantage is insignificant for the short lengths encountered in motorcycle applications.
    Fabian likes this.
  16. jaguar

    jaguar Well-Known Member

  17. Fabian

    Fabian Well-Known Member

    Laser ignition - hmmm, now let me be a little theatrical; throwing on my Dr Evil suit.

    As part of my new (evil) plan for world domination, my bike has been fitted with a Jaguar Laser Ignition, which is pretty fricking awesome.
  18. jaguar

    jaguar Well-Known Member

    OK I finished my testing. Settled on .66ohms which reduced the peak electrical current to half, and I assume increased the spark duration to twice as much. Testing it on the bench both ways generated enough spark at 6000 rpm for the spark to jump from the center electrode all the way over to the side. (because the ground electrode was bent completely away from the center electrode.)
    Real life testing though showed no performance difference except when taking off from a start with a very gradual opening of the throttle. In that case there was some misfires with the resistance in place (between the CDI and HV coil primary).
    Maybe if a manufacturer makes an economy minded street bike with a lean air/fuel ratio then that may be of some use, but on a bike correctly tuned and jetted the best spark is strong and fast.
  19. jaguar

    jaguar Well-Known Member

    Concerning spark duration, this is what Kawasaki did:
    On their street version of their KDX enduro bike they put a 1.5uf charge capacitor in the CDI. But in their dirt-only version of the KDX they put a 1uf in it. Larger capacitance yields a longer capacitance discharge time so that the 1.5uf discharged 50% longer than the 1uf. The drawback though was that at top rpm it charged up less than the 1uf and so gave a weaker spark at high rpm and less engine performance up there.
    How this relates to the Jaguar CDI:
    It comes with a 1uf capacitor which from real life testing is correct if the engine revs up to around 8000rpm. If the engine isn't ported and still maxes out at 5500rpm then the capacitor could be 1.5uf for a 50% longer spark duration for amateurs that aren't good at jetting, or for stubborn people that stick with the horrible stock carburetor.
    I could make this "amateur" version but really my whole goal was to help people maximize the power output, not keep it stock. If you have a Jaguar CDI and haven't increased compression, put on a good carburetor, and ported it then shame on you.
    But if that's you and you want a longer spark without reducing spark current (which happens when resistance is added in the capacitors discharge path) then you can solder this .47uf cap parallel (end-to-end) to the large 1uf cap: 871-B32652A3474J from Mouser Electronics online.
    ps- don't anyone request a video to hold your hand while doing this. Any retard can find the largest part on my CDI and solder another capacitor to it.
    Online soldering tutorials for beginners:

    For a soldering iron I recommend a dual output (20/40 watt) one, # 64-2184, for $23 from Radio Shack. A good cheap .05" diameter solder is available from Radio Shack (locally or online at, #64-015) for $3.
  20. Fabian

    Fabian Well-Known Member

    Now that's the Jaguar CDI option that i wanted - the 1.5uf for a 50% longer spark duration. To hell with 8,000 rpm, because i never rev my engine over 4,800 rpm. I want a brilliant blazing, long duration spark (like an arc welder electrode) when the engine is down on it's knees at 2,300 rpm.

    Can the Jaguar CDI be built with switchable capacitance, so the user can select either the 1uf or the 1.5uf capacitor, dependent on their ignition requirements?