Crankcase vent blocked

[kendunn]

I just bought a lightly used 03 EC250 and have been having trouble fouling plugs. Changed reeds, went through carb, etc and nothing. Someone told me to check the left cylinder/crank/power valve vent to make sure it wasn't plugged and found it had been intentionally plugged off. Anyone know why someone would do this? Could this indeed foul a plug (very erratic fouling, fine for a couple of rides then bam, fouls 2 or 3)? I am of course going to fix this, but it takes a while sometimes for it to show it, so it may be a couple of rides to rear its ugly head. I thought about a crank seal, but the drain plug for the cylinder is clean, and it doesn't seem to use any oil.