[brown7373]

No, I'm not sure it is a ping, but it is some kind of slight rattle and loss of power. f I press harder on the gas, it definitely shows loss of power, and sounds bad and forces me to immediately ease off the gas. I hadn't thought about broken valve spring, but that is a good thought. When it first happened, I got a funny sort of "pop" as I turned the key. It started and idled fine, but all the other symptoms were there.

I haven't done a thorough advance check, but I inspected the wires
and the cap. The vacuum advance works correctly and doesn't leak. I checked advance at idle and the distributor appears to advance correctly (up past the timing marks) when I blip the carb, and it immediately returns back to correct timing at idle.