Extreme pressure inside of my motor

I have a Rancher 350 2002 and it was leaking gas i to my airbox then going into my engine, before i got it fixed it didnt smoke, but then i got it back and it did smoke a blueish smoke, now there is a ton of pressure in my motor and i have to relieve it by cracking the oil cap which sprays oil everywhere, does anybody know what the problem is???? Oh and by the way i'm a new member and i'm not too sure how these forums work.