small Briggs & Stratton lawn mower runs unstable

eddeheerMay 13, 2014

Hi there,

I've run small a B&S lawn mover for two years without any problems. All of a sudden (but after cleaning the machine etc) it began running unstable/irregular. Strange enough when de machine allmost runs out of gaz is starts working great. Filling the tank the same problem appear

I hope this forum wil help me out.

Thanks and regards,
Ed

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mla2ofus

Have you changed the air filter?
Mike

    Bookmark   May 13, 2014 at 10:01PM
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eddeheer

Hi Mike,

I did clean the (foam) air filter because it was dirty and drained with oil. Without result. Even with de air filer out the machine runs unstable.

Thanks and regards,
Ed

    Bookmark   May 14, 2014 at 4:12AM
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mla2ofus

Try running it w/o the air filter. If the problem persists then you have a rich mixture caused by the choke,if it has one, or the carb has a fuel mixture problem. How does it run at low idle?
Mike

    Bookmark   May 14, 2014 at 8:07AM
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eddeheer

Hi Mike,

I'll try this weekend and keep you posted.

Thanks,
Ed

    Bookmark   May 14, 2014 at 1:57PM
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skippymud(NYState z6)

If you can post the Briggs Model, Type and Code, that would help. Interesting that it runs well when almost out of gas.

    Bookmark   May 16, 2014 at 12:53AM
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eddeheer

I tried running without the airfilter. No positive results. The machine still runs slow and unstable.

Its a B&S XC35 (classic)

Thanks in advance,
Ed

    Bookmark   May 19, 2014 at 2:58AM
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mownie(7)

***"Its a B&S XC35 (classic)"***
Well, that is just precious.
But that stuff is just marketing hype.
Look the engine over closely and you will find the "real deal" in identification numbers, most likely will be numbers pin prick etched onto a riveted metal ID plate.
The numbers will be called MODEL NUMBER, TYPE NUMBER, and CODE.
Those are the only numbers that mean anything to a mechanic or parts person.

    Bookmark   May 19, 2014 at 9:14AM
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eddeheer

I think I found the numbers:

9D902 2096 B1 05102751

See attached photo.
Thanks and regards,
Ed

    Bookmark   May 20, 2014 at 11:15AM
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mownie(7)

Having looked at the Briggs parts manual (IPL) for this engine, I suspect that the carb mounting diaphragm/gasket (where the carb mounts to the fuel tank) may have a defect in it which is feeding extra fuel through the main jet by engine vacuum instead of simply pumping the fuel in pulses.
The fact that the engine seems to "run better" just before running the tank empty supports the notion that the carb is feeding extra fuel to the engine.
If a new carb mounting diaphragm does not solve the problem, replace the carburetor assembly.

    Bookmark   May 20, 2014 at 11:48AM
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eddeheer

Hi,

Thanks for the quick response. I'll try to find the parts you mentioned here in the Netherlands.

P.S. do you have a link to the parts manual you refer to ?

    Bookmark   May 21, 2014 at 4:36AM
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mownie(7)
    Bookmark   May 21, 2014 at 11:24AM
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eddeheer

Hi 'Mownie'

I found the diaphragm and gasket and replaced them this evening , together with the spark.
The machine runs great !

Thanks and regards,
Ed

    Bookmark   June 3, 2014 at 1:44PM
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mownie(7)

Glad to hear a good report.

    Bookmark   June 4, 2014 at 12:53AM
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