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Briggs and Stratton 21 HP
mode 331877
type 0730
code 090105ZD

Carburetor.. Orginal should be a Nikki 591736,, That is no longer available and replacement is a Ruixing 594601.
The Ruixing 594601 is what is own the engine now..

The guy i bought the Riding mower from had just put a aftermarket carb on it.. Other than it idled poorly it worked for the few time i used it (winter).. Then one day the thing started leaking gas out the carburetor.. Since it was a 18 dollar aftermarket I did not even mess with it.. I ordered the OEM .. (or as nears as I could get) in the Ruixing 594601.. It has been installed now since 1st of February 2021.. I sold the mower yesterday.. The guy got it home and mowed ,, for an hour with it.. Today he messaged me with a video and the carb is leaking gas out the bottom (or out somewhere and showing out the bottom.. Video was not that clear..
I use ONLY non Ethanol gas and ALWAYS add Sta-Bil to my jugs..

I have to go look at this mower tomorrow.. What could be happening.. 2 carbs about same amount of time... And I have a Craftsman rider with same engine (except CA. rules) with no problems.. A older MTD with Float type carb and a Husqvarna with a Kohler.. and have had no problems with them..

First I believe the John Deere Tech of over 21 years, use Star Tron Fuel Treatment, read above statement.
Carburetor above is correct carburetor for your engine, a Nikki carburetor superceded to part # 594601. The carburetor you have on your engine now is way above your code number, wrong carburetor item 125b, you need item 125. Some Amazon carburetors are manufactured in Asia very cheaply. Jacks Small Engines is a reputable Business, OEM parts, purchase today & have it by end of week, they have over 20 in stock. Be sure to tell them you want UPS to deliver to your home not USPS, otherwise you may get it no telling when. I personally have experienced this in the past not knowing UPS passes off packages to USPS sometimes & I may get package a few days or weeks later. I placed an order last week at Jacks & asked them to please ship part UPS to my home & they did it on time at no extra charge
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did you replace the fuel lines and clean/flush the gas tank?
i wonder if there is debris that is lodging in the needle/seat area and holding it open causing it to leak...

mechanic mark said:

Fuel - John Deere Fuel Treatment

https://www.google.com/search?q=john+deere+fuel+treatment&oq=john+deere+fuel+treatment&aqs=chrome..69i57j0j69i60l2j69i61.19212j0j4&sourceid=chrome&ie=UTF-8

www.lawnmowerforum.com

First I believe the John Deere Tech of over 21 years, use Star Tron Fuel Treatment, read above statement.

https://www.jackssmallengines.com/jacks-parts-lookup/manufacturer/briggs-stratton/briggs-stratton-engine/200000-399999-series/331800-to-331899/331877-0730-b1

https://www.jackssmallengines.com/jacks-parts-lookup/part/briggs-stratton/594601

Carburetor above is correct carburetor for your engine, a Nikki carburetor superceded to part # 594601. The carburetor you have on your engine now is way above your code number, wrong carburetor item 125b, you need item 125. Some Amazon carburetors are manufactured in Asia very cheaply. Jacks Small Engines is a reputable Business, OEM parts, purchase today & have it by end of week, they have over 20 in stock. Be sure to tell them you want UPS to deliver to your home not USPS, otherwise you may get it no telling when. I personally have experienced this in the past not knowing UPS passes off packages to USPS sometimes & I may get package a few days or weeks later. I placed an order last week at Jacks & asked them to please ship part UPS to my home & they did it on time at no extra charge
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Click to expand...

I am not sure of your point.. The Nikki part number, item 125 (which is the OEM carb for this engine but not available anymore)is the same (because it supersedes to Ruixing) as the Ruixing part number, item 125B . Briggs and Stratton parts site will show you the same thing. The old Nikki part number is 591736.. and This current carb is not a china knock off It was purchased from a Briggs dealer and came in a Briggs Box and has the Ruixing insigna etc,,

Scrubcadet10 said:

did you replace the fuel lines and clean/flush the gas tank?
i wonder if there is debris that is lodging in the needle/seat area and holding it open causing it to leak...

Click to expand...

Thank you.. I did and change all fuel lines and the filter.. Tank was removed and flushed well.. That said.. I am still thinking the same as you.. Maybe for sme reason the filter is coming apart... It was bought from a local shop but these days you do not really know what you are getting..

If the problem is debris in the float valve, then it most likely will NOT be a single, solitary piece. Remove the float bowl and you may find an entire collection of smaller particles that made it through the float valve... all collected in the bottom of the bowl. Wipe the bottom of the bowl with a white paper kitchen towel. If it comes out brown then you know rust is getting in somehow.

That's one of the functions of a float bowl... to collect the invaders so that the engine can resist small, localized run-ins with water and debris.

BTW... the debris may be coming from your gas can or from your local gas station. Washing out the mower tank is admirable, but not a guarantee the leaking will stop.

mechanic mark said:

https://www.jackssmallengines.com/jacks-parts-lookup/part/briggs-stratton/591736

https://www.jackssmallengines.com/jacks-parts-lookup/part/briggs-stratton/594601

Click to expand...

Yes ..what I have said all along ... your top link /591736 (nikki) is no longer available and is replaced with your bottom link /594601 ... which is the ruixing carb.. which is what I have..

Born2Mow said:

If the problem is debris in the float valve, then it most likely will NOT be a single, solitary piece. Remove the float bowl and you may find an entire collection of smaller particles that made it through the float valve... all collected in the bottom of the bowl. Wipe the bottom of the bowl with a white paper kitchen towel. If it comes out brown then you know rust is getting in somehow.

That's one of the functions of a float bowl... to collect the invaders so that the engine can resist small, localized run-ins with water and debris.

BTW... the debris may be coming from your gas can or from your local gas station. Washing out the mower tank is admirable, but not a guarantee the leaking will stop.

Click to expand...

of course debris can be coming from anywhere..however, the filters job is to make sure it does not get to the carburetor...

I believe we found the culprit.. I pulled the Carb off and in the bowl were several 'needles eye pieces of light colored debris.. I pulled the float and meter valve out and all looked good there.. cleaned and back sprayed every thing .. put it together with new quality filter and filled the tank.. ran the engine for about 10 minutes.. waited an hour.. No problems ... crossed fingers.. This is next morning and still all good..... Backing to yesterday... When I got to the mower the new owner said it would not turn over with the starter.. (Worried look here)... I did not try with the key but pulled the spark plug and turned over by hand and it unloaded a bunch of gas out of the cylinder.. Then on checking the dip stick I saw it was very liquid and over full.. I decided on a oil change and when drained it was very much loaded with gas.. AHH.. Owner said he had just under half a tank when he stopped mowing and parked it so about a gallon of fuel went out on the ground and in to the engine from that little piece of debris.. Thanks for all the thoughts and helps..

One more question.. How do I get this site to email me when there are new replies..

well I cannot figure it out.. it will set for days with no problem.. then go out and fuel leaking,, engine flooded with gas.. besides 2 new carbs now.. replace fuel lines twice and the fuel line from the filter to card 3 times and 3 filters, 2 of them Briggs and Stratton filters purchased from local small engine shop (pack of 2)... Gas is Chevron non ethanol with sta-bil in it and is not in the machine long enough to cause damage if it were the worst gas in the world.
I also have a Craftsman with almost twin engine to problem unit .. An Ace (MTD) with 14.5 horse L head with similar carb system, A Husqvarna with similar carb set up on a Kohler engine, and a old Craftsman Indy 500 mower with an opposed twin engine, All brought back from the dead All same Gas.. others at this point setting with out use for much longer periods than this problem mower with no fuel issues at all..