Get some copper gasket sealer and take the rear part of the engine off and smear a very very thin layer around where the oring kind of in the corner also you can take out the carb and smear a very small amount around where the O-ring is on the carb, also you can do the same thing with the head gasket. When I say thin I mean realy realy thin, you should be able to see through it like it's almost not even there.