I had a similar problem with fuel just dumping with out the bike running. I discovered that the replacement bowl gaskets expand when exposed to gas. Most likely ethanol in the gas. The gasket expands into the bowl and holds the floats from closing.
I found a person that cuts new gaskets that do not expand, Scott at Ron Fitzpatrick Jeep made the gaskets and has the pattern for these gaskets.
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1965 Honda CP77 — Ulsan Metro City, Rep. Korea
Restored with original parts — Owner: J. Doe