After some careful thought and a little prodding from IanR I decided to do a little work on the combustion chambers. From the vast collection of photo's that Ian sent me, it seems as though the area between the intake/exhaust valve creates some flow restrictions.
I've never done this sort of thing before and didn't want to go to wild as this is not a race engine. So here's the start point...
So I blended the sharp edge around the spark plug area and created some downward swirl to the shape.
Here's all of them done - they are polished with 320 grit rolls and seem pretty good to me.
While I was at it, I decided to flatten the mounting surface...after 2 passes with the file, have a look at this, there's no way this would have sealed long term.
Close-up.
Finished.
