# 4 hp B&S LM engine running too rich



## junkyarddoggie (May 24, 2007)

Hello guys

I am attempting to repair a mower for my sister. I have no idea what she has done with it, other than she didn't take very good care of it. It seems to run rich and carbon up the spark plug fast. I've replaced both gov. springs and still fouls up the plugs, misses and surges quite bit. It will run great for less than a minute with a new plug, but fouls up quickly. I played with the springs and got it to run quite a bit better but it's still not right. I've taken the carb apart, and cleaned it, Pulled the head off cleaned the valves and top of the piston, pulled the flywheel off to check the points and condenser, but there was nothing under there. This engine has the newer style solid state ignition. Any ideas guys? The mower engine is a 4 horse B&S aprox. 6 years old. It's the base model mower, nothing fancy. My Sister has no money, so I would really like to get it running good for her. 
Thanks
Mike


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## 30yearTech (Sep 14, 2006)

Is the air filter clean, it sounds like it's running too rich. The governor spring do not control the mixture. If this carburetor is the diaphragm type it could be leaking around the diaphragm causing a rich running condition.

Post the Model, Type and Code number off of your engine and perhaps we can narrow down the possibilities.


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## junkyarddoggie (May 24, 2007)

*B&S running problems*

The air filter is clean. My dad cleaned right before I got to it, he said it was filthy. The base gasket / diaphragm between the tank and carb was kind of puckered. I pulled it flat and I believe I got it sealed up. I did spray some carb cleaner around the base of the carb while it was running, if it was leaking I would have heard the engine rev up right. I didn't hear any change at all while it was running. My next thing was going back to the carb and check it again. The numbers on the engine are Mod. 10A902 Type 2139E1 Code 99052154

Thanks Mike


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## justin3 (Apr 10, 2007)

Well I can't wait to see what my sister does to her lawnmower when she moves out... Anyhow in your case let me start by saying that those diaphragms never work right unless you replace them, no matter how they look. Don't forget to clean out your tank because part of the tank has to do with the carb.


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## 30yearTech (Sep 14, 2006)

The diaphragm will leak on the inside area of the carburetor and fuel tank, not necessarily on the outside. Spraying carburetor cleaner around this type of carburetor will generally have little effect unless it manages to get into the vacuum area of the fuel pump. The metering tube is submerged in gas so it will not pick up any of the cleaner when sprayed around the carburetor mounting area to the fuel tank.

If the diaphragm is distorted at all you really need to replace it, for it to work right.


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## junkyarddoggie (May 24, 2007)

*B&S Carb.*

Yes,I was starting to think that it was the carb, and that it would be worth looking at again. I'll pull it apart and see if I can get a new diaphragm for it. 

Thanks Mike


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## junkyarddoggie (May 24, 2007)

*got the mower fixed*

Well that was it, the rubber diaphragm was causing the problem. Replaced it this afternoon, and it runs great. I used it to mow the side yard and had no problems. 

Thanks guys
:thumbsup: 
Now that mower is fixed, I can move on to the next project. at one point in this job, I was thinking I might not be able to get my sisters mower running right. I started going through my old junk mower engines to see if I could put together good one for her. Since I got a bunch of that mower stuff out, I want to tinker with one I gave up on a while back. I'll create a new post on that one. 

Thanks again for all the input guys.
Mike


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