Originally Posted by piston slapper
Need model and spec #...
It may have been assembled with the old style head gaskets that were notorious for leaking between the oil drainback hole in the gasket and the cylinder..
Possibly a broken reed valve...but it would be using a lot of oil..
This is my exact thoughts as well the head gaskets. My 25hp did the same exact thing. I replaced them with the new style head gasket and no problem since.
Here you can see where mine was leaking