Hi ,

Just purchased a four year old mower with a 22 hp B&S Vanguard - it appears to be blowing oil out of the carb - runs fairly well but at idle runs a little rough

Hi,
My first answer may solve all, or not. Since you say 22 HP, I surmise that it is a V twin. I would say that the oil problem is caused by a crankcase pressure problem probably caused by at least one blown head gasket. It is causing increased internal pressure that is blowing the oil.
This could solve all, or the second could also be a dirty carb.
Peace,
Clarke