I have an 8 year old Husqvarna 21 in push mower with Honda 160 engine. Last year it began smoking upon start up and it smoked and still smokes until the engine is warm/hot - usually 3 to 5 minutes, then the smoking stops. At first I thought it might be an oil ring but since it stops once hot, I made me think it was some kind of engine casing valve that is stuck until warm. (I am familiar mechanically with overhauling engines as I did this on my dad's farm many years ago.) I cannot find a valve that corresponds to this on the 160 engine.
 
Any help with identifying the possible culprit on the 160 engine? Thanks