Hi Everyone , I Have A 15.5 Briggs & Stratton Ohv Engine Sitting On A 2000 Model Craftsman Riding Mower. I Bought This Mower+engine For A Winter Project. Previous Owner Stated He Could Not Get Engine To Run. First Thing I Did Yesterday I Opened The Carb's Bowl And It Was Real Dirty So I Replaced Carb With A Good Spare I Had Drained Old Fuel , Add New Fuel Pull Choke And Turn The Ignition Key, Acts Like It Wants To Start But It Just Kinda Backfires Thru The Air Filter Housing, Next I Opened The Valve Cover And I See One Of The Pushrods (top) Was Missing The Small Cap That Goes At The End Of The Pushrod And Against The Roker Arm, So I Took Off The Rocker Arm And Install A New Pushrod Cap Put Roker Arm Back On And Still Doing The Same Thing. Starter Acts Like Its Weak When Turning Flywheel (im Using A Battery Charger While Cranking) When I Take The Spark Plug Out Engine Will Spin Great , When Spark Plug In , Engine Will Be Slow And Backfires Thru The Air Filter Housing. Any Ideas Where Do I Need To Check. Im Pretty Good At Cleaning Replacing Parts But Not Good At Diagnosing. Thanks In Advance , Jesse