mcallan wrote:
> Does anyone know the voltages produced by the charge coil, pulse
coil,
> and cdi box on a 1983 it250. I have a nasty high speed miss, and
> resistance test show nothing. Thanks
Typical exciter coil voltages in CDI systems would be around 175 on the
low end to as much as 500 volts. The CDI box wouldn't do anything to
*amplify* the voltage and current, it's just an electronic switch. If
the pulse coil puts out 1.5 to 3 volts that would be enough to trigger
the silicon control rectifier that grounds out the exciter coil and
collapses the field in the ignition coil. Simple non-CDI electronic
ignition systems can be triggered with a 1.5 volt "D" cell flashlight
battery...
If your CDI system is working at all, it's probably OK. Solid state
ignition systems are like that, they either work, or they don't...
But I would recommend running the engine at night in the dark to see if
the spark lead is defective and sparks are jumping to the cylinder head
or the frame, or if the spark plug cap is doing that trick, losing
voltage that way. Also, trying a smaller spark plug might indicate
whether your CDI was putting out enough voltage, but the narrower gap
might also indicate that the fuel air mixture was too lean...
Also, check all the elctrical connectors to be sure the pins are all
clean and not corroded and that the female sockets are all tight so the
male pins make intimate contact...
One of the weirdest electrical problems I've see was on a 2-stroke race
bike with K-Mart coils. The engine would cut out when the rider tucked
in behind the fairing on the straights. One cylinder would cut out. His
upper bodt weight was pushing the aluminum gas tank down onto the
exposed terminal of one of the three ignition coils, shorting it out.
When he'd sit up, that cylinder would start firing again...
On another 2-stroke, I blamed the factory race kit magneto for causing
one cylinder to cut out at idle. As soon as I would open the throttle,
that cylinder would start firing again. It was just an idle mixture
problem, the cylinder couldn't fire on a weak idle mixture...
If you're getting wet fouling on the spark plug's insulator nose, that
doesn't always indicate that the mixture is too rich, it could be too
lean and the engine might be firing intermittently depositing carbon on
the spark plug for that reason...
Riders troubleshooting what they think are ignition problems often have
carburetor problems, they just don't know it and they try to mask lean
conditions with cold spark plugs and rich conditions with hot spark
plugs...
Hot spark plugs can burn a hole in your piston. Don't ask how I know
that particular fact...
--------------------------------------------------------------------------
About CDI's...
Many orbits ago, my uncle Sam sent me to his Weapons of Mass
Destruction Repair Technician school and he taught me about such things
as Capacitor Discharge Ignition Systems that were used to light the
fires in the turbojet engines of his intercontinental nuclear bomb
carrying B-52's...
It seemed in those days that a Capacitor Discharge Ignition System
needed a honking *big* capacitor to store up a whole bunch of current
produced by a solid state power supply that had some switching
transistors inside and they would make a high frequency singing sound
as the switched on and off rapidly, making electricity to store in that
afore-mentioned capacitor...
And I saw the demonstration and troubleshooting board that students
trained on in order to figure out what was wrong with the system when
it didn't work right. The board had a spark gap inside a glass tube to
keep students from getting electrocuted by the CDI system, should they
get their body across high voltage points...
The CDI fired a huge white spark inside that glass tube and it fired
*slowly* and *loudly*. I remember how the spark went *whock!*,
*whock!*, *whock!* as it fired every second or so...
An ignition system that fires so slowly would work in a turbojet engine
that only needs spark for starting, not running...
But Kawasaki needed the advantages of a CDI system on their high
performance 2-strokes of the late 1960's. The advantage of a CDI is
high voltage, a lot of current in the spark, and a very quick voltage
rise time across the spark plug gap. This rise time can be as slow as 2
to 7 milliseconds...
The problem with the old fashioned Kettering ignition system that used
a battery, points, and an ignition coil was that the voltage rise time
was much to slow. While the ignition coil could produce up to 35,000
volts, it would take as long as 50 to 100 milliseconds for the voltage
to rise that high. And, if the insulator nose of the spark plug was
covered with carbonized oil from slow running in a 2-stroke engine, the
voltage might leak away faster than it could build up, and the cylinder
would misfire...
Engineers of battery-and-coil ignition systems were faced with having
to make a compromise between ultimate spark plug voltage and voltage
rise time.
They designed very small coils which had less copper wire and less iron
core material. Though the ignition coils of Japanese high RPM
motorcycles might only put out 9,000 to 12,000 volts with a 1000:1
turns ratio, the voltage would rise quickly enough to save enough
voltage to fire the plug...
The down side of low voltage ignition systems like that is that the
ignitable range of fuel air mixtures becomes more narrow and the spark
plugs have to be cleaned and regapped frequently and the spark likes to
jump from the sharpest edge of the center electrode to the ground
electrode so that center electrode needs to be filed flat and the plugs
regapped frequently...
Back in that era, many orbits ago, our cars had battery and coil
ignition systems and the drill every winter was to install new plugs,
points and condensor and give the engine an electrical tuneup, just so
that it would start at all on a cold winter's morning...
A graduate of one of the Air Force's mechanical tech schools told me,
"If your car won't start and it acts like there's something wrong with
the *carburetor*, fix the *ignition system*, there's nothing wrong with
the carburetor...
These days, the reverse is true, if you think it's an ignition problem,
look into the carburetor and see what it's doing wrong...
Kawasaki had the first really high tech solution to the weak sparks
that plagued us with our early model Japanese bikes...
Kawasaki's first whining box CDI ignition system didn't need any
exciter coil at all, it made its own 250 to 400 volts to charge up the
capacitor.
Kawasaki could use special "surface gap" spark plugs with no insulator
nose at all, the system had enough voltage to fire across a flat
surface to the
shell of the spark plug. Nobody has used any whining box CDI's since
then though, they have all gone to the exciter coil, pulser coil, SCR,
and ignition coils in their CDI systems...
And nobody even seems to know that CDI once stood for Capacitor
Discharge Ignition. Are there even any big honking capacitors in a CDI
system anymore?
They aren't even needed in a system that has a high voltage exciter
coil enegized by a spinning permanent magnet...<!-- ~MESSAGE_AFTER~ -->
>> Stay informed about: Ignition output voltages 
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