# What cause occasional backfire and after you turn off motor?



## orangputeh (Nov 24, 2016)

I have a HS55 that runs pretty good. previous owner just had it services, new plug , oil, etc. We tried it out in this drive and everything appeared fine but did not run very long.

Last night we got about 8 inches so I thought I'd try it out. It ran well at first, did several passes. Then it backfired so I shut it down. After it stopped , it backfires again.

So I know I should look at plug and gap first. If that is not the problem what should I look at in order?


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## Normex (Feb 21, 2014)

At first I wouldn't worry if it did only one or two backfires while running but it sounds like your timing might be off just a bit.
As for backfiring when shutting it is not a big issue since when shutting off the intake valve get a rush of gas and the exhaust valve or the surrounding has a tiny bit still red from running before which ignites the incoming gas with the intake valve open.

Or the key on the crankshaft may be just slightly bent which would allow backfiring when engine is running but first you should run it some more when snow blowing and see if it reoccurs many times while running.

For now Good Luck

Norm


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## bad69cat (Nov 30, 2015)

Yeah it's not unusual to have a backfire on a machine that might be running a little rich..... better than running lean. Try to idle it down and let it run slower when you shut it off...... if that still doesn't cure it you might try to lean it out just a touch if the carb is adjustable - and I don'thtink that one is if I remember right......


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## orangputeh (Nov 24, 2016)

Ok. Thanks for the input. Since I just got it last night I am just gonna do my own service and see what I can see.


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## E350 (Apr 21, 2015)

What *bad69cat *said. And what it says for my 1980s Craftsman riding mower: "Reduce the throttle to minimum before shutting it off to reduce backfire," or words to that effect.


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## 43128 (Feb 14, 2014)

if it only bakfires when shutting it off, i wouldnt worry about it. if it backfires but only when the engine gets hot it may be a bad ignition coil


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## JnC (Feb 21, 2014)

Check to see if water/snow is getting into the carb some how someway. I ran into a similar situation last year with an HS828, realized later that water/snow was getting into the air inlet as the dome cover for intake was missing rubber gasket from its lip.


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## orangputeh (Nov 24, 2016)

JnC said:


> Check to see if water/snow is getting into the carb some how someway. I ran into a similar situation last year with an HS828, realized later that water/snow was getting into the air inlet as the dome cover for intake was missing rubber gasket from its lip.



all good tips.....thanks . will get on it and report back if I find something that will help another with the same problem in the future.


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## alphaboy123 (Oct 27, 2016)

You might want to drain the carburetor bowl. My HS55 was running rough and decided to drain the bowl. Added some Seafoam to the gas and it seems fine now.

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## CO Snow (Dec 8, 2011)

Don't start doing a whole bunch of stuff. Owner's manual for my blower and riding mower both say to run at slow idle before shutting off. Do that before you do anything else.


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## alphaboy123 (Oct 27, 2016)

CO Snow said:


> Don't start doing a whole bunch of stuff. Owner's manual for my blower and riding mower both say to run at slow idle before shutting off. Do that before you do anything else.


yes i agree.. i always lower idle.

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## drmerdp (Feb 9, 2014)

Yup, it's a good idea to idle the engine before shutting it off. Most engines only kill spark for shut down.

The engine continues to reciprocate to a stop after spark is removed. The fuel air mixture gets compressed and exhausted into a hot muffler then ignites "pop".

If it isn't popping while running then I wouldn't sweat it. Never a bad idea to check your valve lash though.


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