In THIS case, the stock HONDA air filter will flow nearly the same amount of air as completely removing the air filter, whereas the Briggs & Straton filter restricts air flow and makes the jetting richer as can be seen by the 2 blue air/fuel mixture lines in the graph.
--We didn't expect this by the appearance of the filters, but these runs were back-to-back, and both the removed filter runs and Honda filter runs made the best power.
--The Green lines were with Honda filter, Red lines are No filter, and Blue are Briggs & Straton.
--All runs were made with a modified air box cover to increase air flow, and were using the same main jet.