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Old 08-20-2008, 01:23 PM   post #1 of 9
tadigiacomo
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Question Briggs & Stratton 12.5 hp - Gas getting into oil

Hi all,

My father-in-law (per my advice) purchased a B & S short block replacement for his 12.5 hp tractor engine. The original model number escapes me, but it is something like 286707, or 28A707. I did the assembly for him, installed the engine, and got it running. It was running great, but he is getting gasoline in the oil. I removed the carburetor (it's a Walbro), disassembled it and cleaned it. I cleaned the needle and seat, thinking that maybe it was not closing properly, thus letting gas drain into the cylinder. The problem remains.

My question is: what is causing this? The engine runs great. My first thought is the carburetor. Should I have him purchase the rebuild kit and rebuilt it? Is it possibly another, bigger problem? How can I diagnose this?

Your thought are welcome and appreciated. Thanks!

Tom D.
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Old 08-20-2008, 01:45 PM   post #2 of 9
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Default Re: Briggs & Stratton 12.5 hp - Gas getting into oil

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Originally Posted by tadigiacomo View Post
Hi all,

My father-in-law (per my advice) purchased a B & S short block replacement for his 12.5 hp tractor engine. The original model number escapes me, but it is something like 286707, or 28A707. I did the assembly for him, installed the engine, and got it running. It was running great, but he is getting gasoline in the oil. I removed the carburetor (it's a Walbro), disassembled it and cleaned it. I cleaned the needle and seat, thinking that maybe it was not closing properly, thus letting gas drain into the cylinder. The problem remains.

My question is: what is causing this? The engine runs great. My first thought is the carburetor. Should I have him purchase the rebuild kit and rebuilt it? Is it possibly another, bigger problem? How can I diagnose this?

Your thought are welcome and appreciated. Thanks!


Tom D.
************************************************** ****
Tom - If you haven't already, you might try removing the float and check to see if it will actually float.
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Old 08-20-2008, 02:14 PM   post #3 of 9
Bill Kapaun
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Default Re: Briggs & Stratton 12.5 hp - Gas getting into oil

Did you flush the fuel line when you had the carb off?
Often, when removing the line from the carb (or changing a fuel filter etc.) crud breaks off inside the line. Hook everything back up, turn on the gas and the crud gets flushed right down into the needle & seat.
I learned that one on my first couple carb jobs, 40+ years ago.
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Old 08-20-2008, 04:12 PM   post #4 of 9
Walt 2002
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Default Re: Briggs & Stratton 12.5 hp - Gas getting into oil

Like Bill said, plus I would install an inline fuel shut off valve and use it every time the engine is stopped for more than a few seconds, never know when a speck of something is going to lodge under the float needle.

The EPA in its' wisdom, mandated that mfgs. due away with the "weep" hole in the carb air intake of old. When the float needle leaked on these, it dripped out on the ground/floor, you saw it, smelled it, and did something about it. Now it leaks into the cylinder and on down into the oil and ruins the engine unless you catch it. ALWAYS check the oil level before using the engine and high level must be checked out perhaps even more than low oil level.

NO, there is not anything else wrong with your engine.

Walt Conner
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Old 08-20-2008, 07:04 PM   post #5 of 9
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Default Re: Briggs & Stratton 12.5 hp - Gas getting into oil

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Like Bill said, plus I would install an inline fuel shut off valve and use it every time the engine is stopped for more than a few seconds, never know when a speck of something is going to lodge under the float needle.

The EPA in its' wisdom, mandated that mfgs. due away with the "weep" hole in the carb air intake of old. When the float needle leaked on these, it dripped out on the ground/floor, you saw it, smelled it, and did something about it. Now it leaks into the cylinder and on down into the oil and ruins the engine unless you catch it. ALWAYS check the oil level before using the engine and high level must be checked out perhaps even more than low oil level.

NO, there is not anything else wrong with your engine.

Walt Conner

My grandpa had one doin the same thing and he never had anytime to fool around with it so he just put a shut off on the fuel line. eventually the carb stopped leakin fuel into the oil. my guess is whatever was in the carb causing it to do that worked its way out.
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Old 08-20-2008, 09:45 PM   post #6 of 9
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Default Re: Briggs & Stratton 12.5 hp - Gas getting into oil

It sounds like the float is not closing. It could be the float or the needle. Check the float first. If it's not that, I would get the rebuild kit and a new inline fuel filter. Good luck!
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Old 08-22-2008, 04:16 PM   post #7 of 9
tadigiacomo
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Default Re: Briggs & Stratton 12.5 hp - Gas getting into oil

All,

Thanks for all the great suggestions and info! I will take that and get this fixed once and for all. I like the fuel shutoff valve idea - I just hope I can get him to remember to use it. I think I will do that first, then look into getting a rebuild kit. Thanks again!

Tom D.
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Old 08-22-2008, 10:01 PM   post #8 of 9
Stan the Air Man
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Default Re: Briggs & Stratton 12.5 hp - Gas getting into oil

The problem is a sticking or dragging float needle. I do not see a shut-off valve as a solution. Here is a tip that often fixes sticking or dragging float needles or needles that do not seat. With the plastic inlet seat removed, if installed, polish the needle cavity. I make a polishing tool using a wooden meat skewer with one end wrapped with NEVR-DULL metal polish. The wrapped tip should fit tightly in the needle cavity. Chuck the skewer in a drill and insert the end wrapped with the NEVR-DULL in the needle cavity. Operate the drill slowly several seconds and the needle cavity is usually clean and polished. If you do not have NEVR-DULL use a wooden skewer, wrap the tip with cotton then saturate the cotton with the metal polish of your choice.

Install and set inlet needle and float. Place a few drops of solvent or fuel on the inlet needle. Pressures test the needle seat by inverting the carburetor and applying 5-15 PSI air pressure to the fuel inlet fitting. A seat that functions properly should hold the pressure. Move the float with your finger and observe that it moves freely.

I do this to every carburetor I rebuild and rarely have problems.
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Old 08-23-2008, 09:10 AM   post #9 of 9
Walt 2002
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Default Re: Briggs & Stratton 12.5 hp - Gas getting into oil

"The problem is a sticking or dragging float needle. I do not see a shut-off valve as a solution. "

A shut off valve is good insurance for anyone to have. As a former Air Force person, you should be well aware of the redundant backups typically used by the Air Force and others. I would note that a shut off valve was standard equipment for LBs from the 60s at least until just recently when they got too cheap to put them on (many people are adding them including myself) and were also used by may other mfgs. Dixon Riding mowers for example which used at least 3 different brands of engines.

Walt Conner
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