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Jeremy R.
Jeremy R., Technician
Category: Small Engine
Satisfied Customers: 9020
Experience:  15+ years of experience and a business owner.
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I have a John Deere riding lawn mower, model LA105. It has

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I have a John Deere riding lawn mower, model LA105. It has not been used much and is only two years old. I think I have about 12 hours on it. The battery is now dead, since I have tried to start it, but is fine when checked. I believe my problem is old fuel. Can you tell what I need to clean or replace for bad fuel?
Thank you,
Hi, My name isXXXXX you for letting me try and assist you with your problem.
I have to say that you are probably going to have to buy a new battery.
A battery that has sat for 2 years is going to be junk.
You can put a charge back into it but it's ability to hold that charge and provide the amps needed to crank the engine over just won't be there.
If you take that battery to any auto parts store they will test it for you with a load tester for free and tell you if it's any good for sure.
I would venture to say with pretty good certainty that it's not.

But then when you get the engine to crank over and it won't stay running the issue is most likely going to be a dirty carb but could be just bad old fuel.
In that case you have to siphon the old fuel out of the tank with a hose and replace it with fresh fuel.
You can remove the fuel feed line from the side of the carburetor and cranking over the engine will flush fresh fuel from the tank through the lines and the fuel pump.
It will be dark brown after 2 years and you'll know you're getting fresh gas when it goes more clear in color.
If you have an inline filter by the carburetor you should replace that with a paper element filter. Not a screen filter. A screen filter will still let debris into the carb and I never would recommend that.
Then once you have fresh gas to the carb.
The bowl of the carb needs to come off.
There's a center bolt in the bowl on the carb that will let the bowl come off.
You will need carb cleaner to spray around the float pivot and the needle valve above the float to disolve the gum and varnish.
Spray through every hole you can find at this point.
Put the bowl back on and see if it will fire up.
It should run, but if it runs rough you will need to take the entire carb off the engine and disassemble it completely to clean every passage in it.

This may sound daunting but it's not really that bad if you have some basic tools and a way to siphon the old fuel out of the tank.
Let me know if there's anything else I can help you with.
Customer: replied 4 years ago.

Thank you for your answer! I think I may have mislead you on the time the mower has not been used which has been about three monthes. I purchased the mower about two years ago. However, I believe your answer still covers the issue unless I hear further from you. I never have had an issue with the mower with exception to a backfire occasionally when I turn it off.

Yeah I still think your battery is probably shot. Getting 1 year out of a lawn and garden battery is about their limit most of the time.
I'd start with the battery. 3 months isn't really that long for a mower to sit so it should run on the fuel that's in it.
The backfire on shut down is a common trait to mower engines.
To reduce it as much as possible idle the engine down for 15 seconds before turning the key off.
The backfire is unburnt gas igniting from the heat of the exhaust causing the backfire.
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