My 2012 850 backfired with my stock and k&n filter, something to do with break in period, I have 650 miles on it now, I run k&n filter and it runs great, no backfire issue at all
backfiring is common in the 850 for the first few hundred miles or so. Nothing to be worried about. Hotter plugs will help with fouling and may stop some of the backfiring though.
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