Welcome to the forum Tom! 
Unfortunately your not the first to have issues with a Briggs air filter not doing it's job. See link below:
Briggs & Stratton 26hp ELS air filter problem - MyTractorForum.com - The Friendliest Tractor Forum and Best Place for Tractor Information
Unfortunately your not the first to have issues with a Briggs air filter not doing it's job. See link below:
Briggs & Stratton 26hp ELS air filter problem - MyTractorForum.com - The Friendliest Tractor Forum and Best Place for Tractor Information