Why does my Countax/Briggs & Stratton engine smoke ?

My countax ride on is powered by a Briggs & Stratton horizontal 16hp engine. The engine runs fine with plenty of power, a bit noisy due to the rubbish silencer, but the problem is, almost as soon as I shut it down to tickover, it smokes like a wet bonfire until I can barely see the other side of the lawn. The smoke is a blue-ish oil smoke rather than a black fuel smoke. I don't really want to strip the entire engine if there could be a simple explanation such as valve stem seals or something similar.I can't see it being rings or anything that serious because it runs so well without smoke when the power is on.
Can anyone shed any light on this problem & save me some work.
Model 280777, type 0646 A1.
Greatfully yours, Steve.

Stephen G
March 2009