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simpleman

Why the backfire

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All very good theories, and I'm first to admit, mine is an amateurs theory.

As for backfiring on start up, does it coincide with a plate of beans from the night before?

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Jim,

I also see the low idle shut down on manuals for other engines as well - like my JD's Kawasaki engine.

TT,

Interesting, somehow that makes sense to me - but, then again, I'm no mechanic like some of you guys are. B)

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All very good theories, and I'm first to admit, mine is an amateurs theory.

As for backfiring on start up, does it coincide with a plate of beans from the night before?

B)

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my C160 12hp k301 with an original style muffler doesnt do it,nor does the C161 with the 16hp k341 with the pepper shaker muffler even if shut off at wide open but i have a 1960 simplicity with a model 19 cast iron 7 hp briggs that does it about every time no matter where the throttle is and it has a harley style straight pipe on it.i also have another tractor with a 16hp cast iron briggs with a very large stack style muffer that does backfire i havent tried idling it down,i will give that a shot.these theroys make sense but im not seeing much ryme or reason (or proper spelling) here with these different engines.the pic is poor quality and its an off topic tractor,im using it to show the straight pipe it backfires thru when shut off at pretty much at any rpm.i will add the with the old cast iron briggs engines carbs,they are notorious for leaking fuel thru without a shut off in the line.

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As for backfiring on start up, does it coincide with a plate of beans from the night before?

Dale, my wife would say it coincides with my heart beating. No beans required!

Kevin

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No idea if this fixed the problem or is just a coincidence. My 312-8 with a magnum12 hp kohler used to backfire every time I shut it down, even if I let it idle for 30sec at minimum throttle.

After I adjusted the valves, it stopped. The exhaust valve was off by a few hundreths of cm before and was therefore not closing all of the way.

After reading your discussion I think the backfiring going away was a coincidence.

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No idea if this fixed the problem or is just a coincidence. My 312-8 with a magnum12 hp kohler used to backfire every time I shut it down, even if I let it idle for 30sec at minimum throttle.

After I adjusted the valves, it stopped. The exhaust valve was off by a few hundreths of cm before and was therefore not closing all of the way.

After reading your discussion I think the backfiring going away was a coincidence.

I'd like to hear a REAL mechanics opinion on this!!!!!!! B)

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I'd buy that...especially if it was an older engine. by te way I am young...so an old engine to me is like 20 - 25 years old.

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I'd buy that...especially if it was an older engine. by te way I am young...so an old engine to me is like 20 - 25 years old.

So does that mean an old engine to me should burn wood and go chug chug chug? B)

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what sound does a tripple expansion steam engine make? B)

CHUG CHUG CHUG ?

Edit, whoever fixed that, THANKS!!!!!! I was going nuts!!! Danged code anyway.....

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hi WH fans! Im a newbie and this is my first post .

I wanted to respond to this post about the backfire issue. My c-141 with Kohler 14 horse had backfired for 18 years and I always felt something was wrong but i lived with it. whenever i get ready to shut it down I always brought it down to idle and let it idle for 30 seconds or so and turned off the key. most times it would backfire.

I have owned this horse since 1990, the last few years i started having fuel delivery problems, last summer it died and i rebuilt the carb, replacing the fuel inlet needle and seat, Now, since the carb rebuild engine runs fine and as a bonus No more Backfire !!

the needle and seat were really worn, original parts I would guess. I cant say that is everyones solution but it worked for me..

cheers...

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B) One thing I would point out is that this phenomenon is almost certainly more likely the hotter the engine is.

If your point gap has the timing to far advanced your engine temperature will be too high and this would tend to aggravate the problem.

:whistle:

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Hi, earlyj57, and :whistle: !

Glad to have you aboard! This is a great place full of interesting people and very useful info.

Have fun!

Duff B)

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Some newer engines have a solenoid in place of the bolt that holds the carb float bowl to the carb body. It is called the anti-backfire, or fuel shutoff solenoid. Two summers ago, when I was ahhh, between jobs, the owner of the lawnmower shop I worked at told me to never shut an engine down on a mower unless it was at full throttle. This was to prevent a backfire that would blow the muffler off! He sold Simplicity and Dixie Chopper mowers.

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We have got a Kohler command 18 which drives a drain jetting pump. This engine will backfire after it has stopped if you don't shut it down and let it idle for a short while, then it's ok. So it's not just old engines but newer ones as well.

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The Briggs 11hp vertical on the 211-4 dad bought new always backfired after shutdown unless the engine was allowed to cool by idling for several minutes before shutting it down. Did it from hour 1 to hour 1700 unless allowed to cool down.

Everybody always seems to theorize that running an aircooled engine at idle speed will overheat it, but the temp decrease on all of mine after idling to cool is very noticable. Remember, the reduced airflow is accompanied by a reduction in the amount of fuel being burned and heat being produced...just don't operate them under much of a load at anything less than full throttle.

That cooling also cools the exhaust too, probably below the ignition temperature of gasoline.

The reason for the delay in autoignition of the fuel in the muffler is that there is not enough Oxygen in the muffler at shutdown to support combustion. The exhaust products - primarilly CO2 - quench the fire that would result from the leftover fuel buildup. After the engine shuts off the outlet of the muffler begins to draw air - 21% O2 - into the muffler. When enough air flows in you eventually reach the Lower Explosion Limit (LEL) and BOOM!

If the muffler has cooled sufficiently that you're below the autoignition temperature you will avoid that explosion.

I am pretty confident of the above explanation, now time to shoot from the hip :banghead: ...

I think Karl's 1/2 throttle solution may be either providing excess air to the unburned fuel in the muffler - beyond the Upper Exploion Limit - or the increase airflow from the open throttle is also providing cooling air to the system. I'd bet that the trick only works well in the 2nd instance if the engine isn't super hot from working really hard prior to shutdown since that residual heat has to go somewhere.

You might get around this problem with no cooling/idling if you switch to premium gas. Premium gasoline ignites at a higher temperature (that's what "Octane" is supposed to empirically describe) and perhaps won't autoignite in the muffler. Just a guess...

Interesting topic!

Steve

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i have a 16hp twin briggs that does the same thing also. I figured it was unused fuel but now i understand exactly why. Good info. :hide:

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