I just got off the horn with TCM asking about if any improvements have been made in the O-200D regarding the leading problems that may help our vintage engines. The guy seemed quite candid. He claims there were no changes to the cylinders except for tapering the barrel fins, so nothing that would affect leading.
The valve guide clearances were changed in ~2000 for a bit more clearance. Those of us with cylinders that haven't been touched since before then should consider having them reamed. That should only add 2-3 hrs to do whenever other engine work is being performed. He suggested that just reaming the valve guides every 2-300 hrs has pretty much solved the problems especially in flight schools. He's aware a lot of schools do use autofuel to reduce cost.
The O-200D engines are to be approved for autogas by TCM although A and B engines are not. He also told me a new design 200 size engine (He gave me a more specific number but I didn't write it down) is in the works but will only be certified for LSA.
Since I had my valve reamed my engine does run smoother. I suspect I've had a tight, lazy valve all along.
