I'm working on a 28mm Mik set-up on a stroker (big bore) animal currently. It's what I prefer with big valves and ratio rockers.
Spin, if you're getting too much fuel in the oil, it's almost gotta be drilled too rich on the bottom end (like a flathead pattern.)
I use the 304wx/a on limited with stock valves. I don't think it's enough carb for big CI opens, BUT, it will likely cure the over-fueling problem.
Tillys don't like to be idled, I don't care who drilled them. It's just a design thing. I suspect that the washing down of the cylinder is caused by too much idling and low part throttle. Avoid that as best as you can. As for oil -- stick with what you know works best for your application. Personally, I like Briggs 4T. Good ol' FHS 62R is a close second.
Jon, Thanks for sharing your insight. Much appreciated. I've never had much luck in epoxy and redrilling, but I've also not tried that particular product. As much as I hate to, I may have to go back through some old flathead carbs and try it now.
Thanks and God bless,
Carlson Racing Engines
34 years of service to the karting industry ~ 1Cor 9:24