[ByronRACE]

Causes of blow-by:

-improper bore finish, rings don't seat during break in
-mixture too rich, rings don't seat during break in
-wrong ring package
-wrong piston to bore clearance
-rings installed wrong
-excessive ring end-gap
-detonation damage (rings, ring lands, pistons)

But what is "excessive" blow-by...are you sure it isn't normal? All engines have blow-by.