Briggs & Stratton 12.5 HP Riding Mower (Snapper)

Hi! Hope in the right forum here.
I have a Snapper riding mower bought in 2009. Recently replaced all the filters, changed oil, installed new spark plug and new blade. Also filled with new gas (no-ethanol). A week later I started having trouble with it. It started missing very bad and black smoke emitted from the exhaust (way too much fuel). I then pulled the carburetor off and checked it out real good and cleaned it. I realized the choke (butterfly valve) was not springing back as it should. Took the carburetor to a small engine shop and they put on a new choke spring. Thought that would fix the problem, so I reinstalled everything. I then started the engine (without choking it) and it purred like a kitten. I gradually advanced the throttle to about midway to rev the engine. It ran very good for a couple minutes, then all of a sudden it started sputtering and blowing black smoke from the exhaust, then went dead. I tried again later and the same thing happened. It's as if it is getting too much gas all of sudden by itself. I'm at a loss as to what is going on and would really appreciate some advice from anyone who may know about Briggs & Stratton engines.
12.5 HP Model: 219907-0131-B1. Thanks for any help here. Please reply.

Sounds to me like the float needle is not closing the float bowl inlet. Do you know if the shop replaced the float needle and seat when they had your carb. If it has the Walbro carb and if they just replaced the needle that may be your problem.

This is a Nikki Carburetor. No, the needle was not replaced. I'm not sure what you mean by "seat". Do you think I need to get a new float and needle for this carb? Could that cause the sudden flooding of the engine with fuel? Please respond and accept my thanks.

Any time I rebuild a carb after cleaning, I replace the float needle. Your Nikki carb has a nonreplacable seat. If the needle is worn it will not properly close off the fuel inlet and thus cause a flooding problem, such as you describe. This is what I think happened. Your engine has a fuel pump. When you started the engine, it ran normal at first, but when the seat did not close the inlet fuel level in the float bowl rose causing a rich condition (black smoke) and chocked off the engine. I would remove the carb, have it ultrasonically cleaned or give it a 24 hour soaking bath. After drying, rebuild with carb kit #796184. This manual might also help you.

http://dl.dropboxusercontent.com/u/12502267/B&S Service Manuals/10_276781SingleCylinderOHV.pdf

Rivets said:

Any time I rebuild a carb after cleaning, I replace the float needle. Your Nikki carb has a nonreplacable seat. If the needle is worn it will not properly close off the fuel inlet and thus cause a flooding problem, such as you describe. This is what I think happened. Your engine has a fuel pump. When you started the engine, it ran normal at first, but when the seat did not close the inlet fuel level in the float bowl rose causing a rich condition (black smoke) and chocked off the engine. I would remove the carb, have it ultrasonically cleaned or give it a 24 hour soaking bath. After drying, rebuild with carb kit #796184. This manual might also help you.

http://dl.dropboxusercontent.com/u/12502267/B&S Service Manuals/10_276781SingleCylinderOHV.pdf

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Thank you so much for your inputs. This has really been helpful in solving my problem. Just to update you, I learned a small part "main jet" had fallen out during my initial disassembly. The part was so small (match head size) that I did not see it. I ordered a new needle valve and the main jet yesterday. However, I am still not certain how this jet fits into the correct place yet. If you have any information on this, I would like to hear it. I got a can of carb cleaner which I will use to clean all the parts. I do not have a compressor, so I plan to use clean air from a can to blow it off. I'll soon know if all this worked as needed. Thank you again for your help.

Charles

Have been unable to find a good diagram on how to install the main jet and seal on your carb. Hopefully this will help. The main jet should be installed on the side of the main nozzle tube. Pages 82-85 are the best steps I can find, hopefully it will help. Maybe some one else can find a good picture of the main jet installed. Sorry

Rivets said:

Have been unable to find a good diagram on how to install the main jet and seal on your carb. Hopefully this will help. The main jet should be installed on the side of the main nozzle tube. Pages 82-85 are the best steps I can find, hopefully it will help. Maybe some one else can find a good picture of the main jet installed. Sorry

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Your help is appreciated. In your above comments, you stated "the jet should be installed on the SIDE of the main nozzle tube". From what I see, it would go into the top of the main nozzle tube. I am forwarding an attachment that show what I am talking about. Any idea how I could confirm this? Thanks again for all your help.

Charles

I'm thinking you are right and I may be thinking of a different carb. I don't have that carb handy so I sent the info to a guy I know who will tell me if I am wrong and you are right, or vise versa. Get back to you as soon as I can.

You've got me looking at this carb and thread again and I just noticed something odd. The carb listed in the parts breakdown for your engine and the carb picture you posted are not the same. Are there any letters or numbers on your carb. We may be talking about two different carbs????

yeah, those Nikki carbs are a pain, if you try to take it apart and blow out the dirt, the jet is just pressed in, and usually gets sent into the next county, the funky gasket curls up like a dead spider, and all of the parts are expensive as hell. Some of those
nikki carbs, the jet just was pushed into the plastic float holder, but assembled, it would stay in place.....