Problem might be, since it is a newer "replacement" carb it doesn't have the spark control valve. Most didn't, but some did. If it isn't there, then the timing advance (which is vacuum based only back then) will be all wrong. Dogged performance. This is the thing you are looking for.
Note: This is a 1940 I rebuilt for a guy in California who had a 1940 lacking this circuit. And note, the carb is not machined to put on on it if it's missing.
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