Briggs And Stratton Backfires Wont Start . I took it apart and inspected it. It stalled out and wouldn't start so i cleaned the mag. Litte help here Briggs 14 5 backfiring FunnyCat.TV from www.funnycat.tv Some carburetors can induce backfire due to the sensitivity of internal transitional passages. Briggs and stratton 17.5 hp won't start and backfires 1) checked the valve clearance. Muffler construction can induce backfire.