"High octane fuel in a low compression engine overheats the poor quality exhaust valve and leads to failure."
TP -- I've been looking for an explanation for my exhaust valve failure (it broke at the friction weld). I thought perhaps I assembled the intake manifold insulator upside down when I installed your twin-fin intake (nope) or the fuel filter I added was clogged (nope) or the spark was weak (nope) or because the exhaust was wrapped (by previous owner, maybe). But living in SoCal I had always used Premium fuel. And it broke on a very hot day while I was in stop-and-go traffic. Your explanation best fits my circumstances. Thanks.
I'm collecting and organizing everything to reassemble my 500cc SB/GG engine. I should have a set of stock cams as I don't remember disassembling the replacement crate engine. If it turns out I do, I'll send them to you.
And I seem to have at least one extra throttle body. Do you modify the throttle body?