[George Miller]

no sign of anything but a few flakes at the bottom and in the clear glass filter at the firewall.
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Don't you think these flakes may be getting over the gas inlet and blocking the flow. It is a gas flow problem for sure. Unless you have two problems.
You need to check gas flow at the time of the problem. Take out the plug at the bottom of the carb, and see how much you get. Should be a steady stream. While your at it check for a nice hot blue spark. one has to be not working right, or both.