High folks. I have an issue with my craftsman mower, which has a B&S 19HP 500cc Intek air cooled engine burning oil on startup. Last year I rebuilt this engine with new piston ring and gaskets and what it does is when first started it will blow oil smoke heavy for about 1 minute then clears up and runs fine after that. If I shut it down and start it up again in a day it burns very little oil on start up but if I let it sit for a week ( I usually mow on weekends) it will do the same thing, blow lots of smoke for about a minute. It is blue white smoke so I kow its oil. Before I start taking this whole thing apart my question is what can be causing this. Is the ring I put in bad? or maybe a leaking head gasket? The thought of taking this thing apart again right before mowing season starts is depressing me. Any advice would be appreciated.