why is my airfilter ful of oil ?

so I took the tarp off the duster yesterday and ive been cruising about a bit
shes allways used oil and been hard to start once warm

I went to check the slack on the throttle cable and when I removed the airfilter about a cup of oil fell out

I cleaner out the breather and installed a fresh PCV valve before I put her away for the winter so what should I look at first ?