B&S 21 hp backfiring

fossil33

Forum Newbie
Joined
Aug 17, 2014
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Hi all,

This is my first time using the forum. I have a Briggs and Stratton 21hp single cylinder OHV engine on my craftsman mower. The engine will start and idles fairly smooth. When I advance the throttle it starts severely backfiring with black smoke out the exhaust. When I throttle back to idle it runs smooth again. Any ideas would be great. Thanks...
 

ILENGINE

Lawn Pro
Joined
May 6, 2010
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First thing to check is make sure the air filter is clean and not clogged, and don't go by appearance only. I have seen filters that look almost new, that were so clogged they couldn't suck air through them.

After that you will need to remove and clean the carb, Most likely either a jet has come loose, or on some carbs there is a rubber stopper in one of the holes, that will come out. The last thing would be a clogged air bleed. those are the holes on the edge of the carb entrance and mix air with the fuel as it is pulled up the emulsion tube.
 
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