Perversely enough, low crown pistons are better for flame propagation. I like the flattest chamber and crown combo I can get away with and that allows timing to be backed down a long way in some instances.
There's a fair amount of carbon for not a lot of miles that could be cleaned out with a wire brush. The side electrodes look like they have run a little hot but are not showing much sign of distress. Try colder plugs and a touch less advance and see how she responds.
You are right that on a 4 stroke we measure static compression and valve timing and pipe design can change that in a running motor.
On a long stroke motor with big old fashioned pistons, actual squish on the exhaust stroke (ie when nothing is being squished) actual running clearance at high revs will be getting close to zero. Unlike a 2 smoke that never has an uncompressed stroke, a 4 stroke has a lazy stroke where the rod can grow as it's not cushioned by compressing gas.
There's a fair amount of carbon for not a lot of miles that could be cleaned out with a wire brush. The side electrodes look like they have run a little hot but are not showing much sign of distress. Try colder plugs and a touch less advance and see how she responds.
You are right that on a 4 stroke we measure static compression and valve timing and pipe design can change that in a running motor.
On a long stroke motor with big old fashioned pistons, actual squish on the exhaust stroke (ie when nothing is being squished) actual running clearance at high revs will be getting close to zero. Unlike a 2 smoke that never has an uncompressed stroke, a 4 stroke has a lazy stroke where the rod can grow as it's not cushioned by compressing gas.