Cracks between the seat hurt performance because they leak shortly after forming and that's lost pressure and a burnt valve...because they grow.
Head gasket was fine, No I never overheated it. Cracks in the seat can slowly siphon out coolant..head gaskets that loose fire ring and combustion leak are what puts pressure into the cooling system.
150cc vs LA 2.02 155cc and 1.88 160cc
That easy, the pushrod pinch is near closed compared to the LA , that's 5 cc right there.
