# Poulan Pro Snow thrower backfires



## sean (Feb 7, 2015)

Hi

I have a snow thrower (poulan pro pr 521) which I have been using fine until today. Today unfortunately while cleaning the snow I left the valve on Start position. I continue cleaning the snow until I realized that I am not getting enough power and black flames have started to come out. Then I realized that my snow thrower is in Start position and not in Run. I changed it to Run position. It ran fine for a minute and it then stopped.

I tried starting it again. It will start every three pull (vs 1 pull before this) and then it will backfire and make loud bang noise... As soon I put it in Run and try to engage, it will stop. It will start again after 3-4 pull but the same thing will happen. 

Any suggestions will be really helpful.

Thank you

Sean


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## Coby7 (Nov 6, 2014)

That's because the exhaust valve is seizing a bit. My suggestion is to start it and let it run at high idle for 5 minutes and hope it will clean itself out.


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## sean (Feb 7, 2015)

Coby7 said:


> That's because the exhaust valve is seizing a bit. My suggestion is to start it and let it run at high idle for 5 minutes and hope it will clean itself out.


Thank you Coby. Just so I understand correctly (I am a noob when it comes to these things) I should put machine in Start position and Start the machine and let it run or after start move it to Run position and let it run and if it makes noise or afterfires then let it do it.


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## Coby7 (Nov 6, 2014)

Start mode is to start. As soon as it is started switch to run mode and let it run at full throttle for 5 minutes. This should clear all the carbon build up on the exhaust valve caused by your OOPS!.


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## sean (Feb 7, 2015)

Coby7 said:


> Start mode is to start. As soon as it is started switch to run mode and let it run at full throttle for 5 minutes. This should clear all the carbon build up on the exhaust valve caused by your OOPS!.


Thank you Coby. I will give this a try and update this thread tomorrow.


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## detdrbuzzard (Jan 20, 2012)

if you know how to check the spark plug take a look at it
it might be fouled


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## sean (Feb 7, 2015)

detdrbuzzard said:


> if you know how to check the spark plug take a look at it
> it might be fouled


That is a good point ... Before start of the season I somehow figured out how to change the spark plug... .. 

If the above does not help then I might as well change the spark plug .. I have one sitting extra...


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## sean (Feb 7, 2015)

OK. So I tried to start the thrower this morning but it would not even start. I can smell the gas now but its not starting. So as a next step I am going to change the spark plug. 

Any other suggestions?


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## sean (Feb 7, 2015)

OK. Just to update the thread. Today I changed the spark plug and BOOM.. One pull start and everything seems normal ... Thank you both Coby and William for providing valuable inputs..


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## Kiss4aFrog (Nov 3, 2013)

It might be a good idea to let it warm up a bit and not use it right away until you have taken the choke off and it's ready to go in the "run" position.


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## sean (Feb 7, 2015)

Kiss4aFrog said:


> It might be a good idea to let it warm up a bit and not use it right away until you have taken the choke off and it's ready to go in the "run" position.


How long do you wait before you put choke to "Run" position? Can I not put choke in "Run" position as soon it starts? I can let it warm up in "Run" position unless you think I should let it warm up while choke is in "Start" position?


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## Kiss4aFrog (Nov 3, 2013)

There is no exact answer because it will take longer to warm up the colder it is outside. Once you start the machine you want to start moving the choke to full off but you also want to make sure the engine is running smoothly.

You do want to take the choke off as soon as you can but if you were running the machine into snow with the choke still on then that is why I'm saying you should let it idle for a minute or two and not start throwing snow until the choke is fully off and the engine is running smoothly.

It's easier on the machine, the machine will work better and you don't run the risk of forgetting to take the choke off.


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