muray lawn tracor with a briggs & stratton motor?

i got a murray lawn tractor with a briggs and stratton motor. the problem i am having is the motor sometimes smokes and runs rough when it starts. then after a few minutes it blows the hose ( i think its the breather hose the comes from the top of the block and runs into the carburator and when that happens it sprays like an oil out of that hose and the tractor runs normal then . any one have any ideas where i should look to see what is wrong? advice would be appericated !