A new idea

[KYGS500E]

I installed a K&N podfilter...

1.  is the breather hose that used to run from the valve cover to the air box supposed to be blocked or just removed and left open???

2.  Could this cause a cylinder to misfire?

3.  I'm pretty sure its supposed to be left off (the hose) and that it wont cause any trouble... but i'm open to ideas!!!

[Egaeus]

I installed a K&N podfilter...

1.  is the breather hose that used to run from the valve cover to the air box supposed to be blocked or just removed and left open???

2.  Could this cause a cylinder to misfire?

3.  I'm pretty sure its supposed to be left off (the hose) and that it wont cause any trouble... but i'm open to ideas!!!

It wouldn't cause your problem.  It just vents blowby into your airbox to be burned. 

What's your jetting again? 

[KYGS500E]

127.5, 40's, 1 washer... with podfilter and slipon

[Egaeus]

127.5, 40's, 1 washer... with podfilter and slipon

We may be getting closer.  Your jetting is too lean for that filter and an aftermarket exhaust.  However, that doesn't explain why one cylinder is fouling.  It should be the other way around. 

Try starting it cold, letting it run for maybe 30 seconds, and taking out the spark plug that's fouling.  See if it's wet.  Perhaps it's too lean to run, and the gas is condensing on the plug, fouling it out.