I have had 3 mowers with the Briggs SINGLE cylinder OHV engines, 2 were the 17.5 HP models, & 1 was a 15.5 HP, both 17s will ALMOST ALWAYS backfire on shut-down regardless of throttle position (fast or idle) it has so far never caused an issue other than scarin the hell out of the animals close-by, the 15 HP, never did it..after nosing around with some other mower owners at the mower store, we came to the conclusion the 17s short pipe BEFORE entering the muffler, was the problem, the "entry" pipe on engines with the muffler located LOW on the frame did not backfire, one fella said he fooled around, changing mufflers to find out for sure, he said installing the mufflers, back n forth proved his theory was true, I have not done this myself, I no longer had the 15 HP, ... anyway, I go along with his assertion, it's the length of the pipe,.. PRE-MUFFLER ! ( see pics of muffler setups )
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