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I'm not sure, if I remove the filter and fin top, I have no other hoses leaving the AB except the big ones to the carbs.



If I recall correctly the AI hose enters from the upper left outside corner of the box. If that's not capped that could be your excess air input.

A positive attitude may not solve all your problems, but it will annoy enough people to make it worth the effort. Herm Albright (1876 - 1944)