yard-man 15.5 hp help!!?

i have a 15.5 hp ohv lard-man lawn tractor 42' cut 7 speed shift on the go. it has a briggs and stratton engine.
model #28n777 type#0642-a1
ok i am getting gas in my oil. i removed and replaced the spark plug, air filter, float, and changed the oil. when i remove the air filter and start the tractor gas and oil shoot up like a frikken guiser out of the first hole. if anyone has an idea please help. thanks