Greetings . . .

I got a referral to this piece from '17 over at Mac's Motor City Garage.
It features a video of a running Briggs L-head engine with a clear head:

The author runs three different fuels. The soaking-wet-rich alcohol run is most peculiar.

regards,
stock49

The flat (uncontoured) replacement head completely removes all of the patented Ricardo features that made the flathead engine successful. There is no quench surface, no turbulence, just a open hole.
What you see is nothing like combustion in an actual SV engine.

Perhaps panic - but I think you are holding the bar a bit high (then again you always do).

Even if the 'window' head doesn't include all the best engineering features of a side-valve design it does reveal the essential elements of 'flame-front' travel from the combustion chamber into the cylinder - the swirl of the exhaust - and the sometimes foggy intake stroke. And for the me the fact that the super rich alcohol mixture even lit was amazing.

Charles Franklin designed a nearly identical combustion chamber for Indian Motorcycles before Recardo and never bothered to patent his designs...They just beat the competition... He really understood how to make a flathead produce power..