I have a 2001 yz80. The spark seems weak. I tested the coil and its fine. I tried it with the kill button disconected, it didnt help.How do I test the stator and cdi? Am I on the right track?

Yes the CDI unit, the sensor that makes it fire or bad wiring connections even to the ignition switch and kill-switch..

https://www.google.com/search?q=Cagiva+canyon+500++weak+and+intermittent+spark

I found a Service Manual but it is in Italian!

https://www.manualslib.com/manual/1054149/Cagiva-1997-Canyon-500.html#manual

..

plugs will not spark under compression if they are faulty or the HT lead id off too high a resistance. or mixture is incorrect
In the real old times when plugs were cleaned and tested one of the tests were to test spark in a dry compressed air chamber where if there was a problem they failed to spark
as you have fitted new plugs it comes back to the ht lead
they are carbon tracked lined internally, the connection for the plug and cap is just a steel pin shoved up into the carbon track
try using copper ht leads where the copper wire comes out to the connection
there could be a valve seating problem or weak valve springs on that cylinder that is not allowing proper seating under compression
if you have 2 carbies then the float level for that cylinder may be too low and under load starving for fuel

Okay. You have eliminated the plug. Now disconnect the coil kill wire and try for spark again. Also check grounding between the coil laminates and the cylinder with you ohm meter should read zero.

If grounding okay and with the kill wire disconnected you still get no sparks then replace the coil pack as it probably a failed internal trigger which can not tested for.

Test the Coils . The coil produce the high voltage for wire plugs+spark plug+motor. If the coil is defective you ignition system can be wrong. see the diagram attached.
God bless you

Sounds like an ignition module/coil problem.

weak spark can indicate bad coil,,,correded wires,,,or grounding of the ignition circut,,in which case you would have No spark,,,simple things first,,,check your wired to the plugs,,some have removable plug caps,,and many times,,corression interferes with strong spark,,,coil testing must be done at a service provider,,,wires can be grounded,,expically if you have dumped the bike and the handle bars have be dissloged somewhat,,,check the kill switch for damage inside..

replace your ignition coil mate, i had a problem like this on my NSR, replaced the coil and i have a full strength spark :)

A yellow spark is usually a sign of a weak coil, change that, it should cure the problem, if not, then further testing is needed.

it does sound like you have a plug lead out take one off the spark plug and plug another spark plug in to it place the plug to earth and crank the engine over there should be a spark there
also get a compression test done because if there is a brake in the head gasket between 2 cylinders then it will run rough and possably misfire

check kill switch ? look at coil wires see if they got rubbed into ? if the are not broken or become disconected then you need to take coil to your local lawnmower shop let them test it with and ohm meter ? they rarely fail thoung ? hope this helps?