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my mower is backfiring when i shut it off it's a B & S 20 hp twin fire

Do you have the mower on open choke or a high idle or low idle?

it's usually in low idle when i shut it down

it has a pull out choke on it the mower was never used much :confused2:. it does surge a little bit when idling. i did replace the plugs as well

. You know the basics

Don't know why the other part didn't show up but as I was saying! Need to know the basics like model I gather its a vtwin 20hp

i'm lawnmower stupid lol haven't a clue what to do .

yes it's a V Twin 20 hp 1996 model MTD yard machine

Normally it would be your idle speed at shut down, but you say you are in low! And the plugs are new at the right gap setting as well I take it.

yes i set them before installing them, i was also told to try letting it idle for 30 to 60 seconds before shutting it down that make any sense to you ?

i was told to try letting it idle for 30 to 60 seconds before shutting it down does that hold any truth ?

O yes definitely! At least 30 sec. Just burning off the extra fuel that way. Is it hard to start?

yes sometimes it's hard to crank . but not as much since i changed the plugs

Have you ever done or had to do a valve adjment

no . not to my knowledge, i'll try the 30 to 60 second shut down first but right now i gotta head to work thanks for your time and advice

I bet this is one if not the main problem, the valves aren't in adjustment, and you should check every year anyways, the do get loose which cause this and mainly a hard starting issue

Look into an adjustment as well

More often than not, a "backfire" when shutting down is caused by glowing carbon in the exhaust system (piston, head, ex port, pipe, and muffler). As you turn the ignition off, and as the engine coasts to a stop, it is still taking in fuel and the unburned fuel is exiting out and into your muffler. The muffler "might" have glowing red hot carbon in it and a backfire is a result. Also check your exhaust manifold gaskets which might allow air to enter making a backfire even more prevelant.

ok thank you guys for your assistance i really appreciate it. :thumbsup: