Good news! When I tried it on the lake today, the boat ran well all the way to full throttle. Last time out, I had established that the reason the boat would not get up on plane was the choke jamming partly closed. But even with the choke fully open and the boat up on plane, the engine would miss at higher rpms.
Since my last post, I replaced the spark plug wires (with NAPA Belkin Max marine wires), replaced the filter in the fuel pump, and replaced the top half of the carburetor (including the flame arrestor bracket, choke assembly, float, and accelerator pump).
So, I have no exact evidence as to the cause of the miss. I don't think it was the fuel filter in the fuel pump (the old stone filter looked perfectly clean), but who knows. There was no visible damage to the spark plug wires, but there may have been damage inside a wire. I noticed that the factory had routed several wires very close to the throttle shaft; when that moved it could have pinched or stressed a wire.
Maybe it will be good for another 30 years. After it's good performance today, it received an oil and filter change and full winterization.
Thanks for all the suggestions.
