A little off topic, sorry, but with the YS engines the only reason not to run a little castor is the diaphram in the regulator, right? The cam, lifters, and rest of the engine could benefit from the castor just like a Saito or OS 4-stroke it seems like. We run castor in the perry and other pumps and regulators. I'm going to try the bit of castor in my YS 70 but not let any sit in the diaphram over the winter..... and see how that works....

Ernie Misner