heres a little sumthin i copied and saved from another members post....................
Your intermittent spark problem is quite likely due to a bad ignition coil. Many times, the high-tension lead (heavy wire that goes from the coil to the spark plug) develops an internal break. Coils can also develop an internal short or open circuit. Either of these faults will result in an intermittent spark at the plug. The coil only fires when the bad connection happens to be made. Which isn't very often, as I'm sure your exhausted right leg can attest.
Do this: Turn the keyed ignition switch (if used) and handlebar switches 'ON'. Unhook the spark plug wire from the plug and remove the spark plug from the engine. Next, find that one-and-only orange wire that attaches to the coil. Unplug it, and go get your 12V test light. (You can buy one for about $ 15.00 at the local auto parts store, or Sears, or....).
Stab the plug on the orange coil wire with the pointed end of your test light. Ground the other end of the test light (with the wire/clamp) out against the engine. Be sure you have a SECURE connection. Now, kick the engine over and watch the test light. The bulb in the test light should blink once for every revolution the engine makes. In other words, the light should flash 'in sync' with the rotations of the crankshaft. This test will tell you whether or not you're getting the required 12 volt 'signal' from the CDI box to the coil every time the piston reaches TDC. If the light blinks steadily, replace your coil. It is defective. The CDI box is sending its 12V pulse to the coil, as it should, but the coil is unable to properly transform it.
Nothing, or an inconsistent blink of the test light, indicates that your ignition coil is not recieving its proper trigger pulse from the other components of the bike's ignition system. Time to pull out the ohm meter and do some resistance checks on the exciter and trigger coils. I'd also test the ignition coil for good measure, just to be sure that it is indeed still good. If these coils test OK (see a Clymer manual for the resistence specs), all connections are clean/tight, and you can't find any bare wires that are accidentally touching the frame, replace your CDI box. It can be ruled faulty if everything else in the ignition system tests good.
