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Discussion Starter · #1 ·
Hi, I am sorry if this has been covered before but I couldnt find anything doing a search.

I have a 4HP Briggs mower(it was free and has been outside all winter), starts and runs rough, idle surge. The fuel mixture seems very rich , and burns through a tank of gas in about 20 minutes. Is there anyway to adjust the mixture or should I purchase a new carb is there something I should check first.
Thanks
jeremy
 

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Re: 4HP Briggs - Rich mixture

Hello Jeremy3ff

The problem with your Briggs mower burning too rich can be from from several factors. The first thing you should do before spending cash on a new carburetor or any other components is to visually inspect them for cracks, burns, or any other physical damage. Once your satisfied that everything seems in place, the next step is to remove the air filter assembly and inspect it for deposits that have blocked the air filter. On some models the filter looks like a sponge, you can clean it by soaking it in gasoline if not use compressed air and blow out the deposits from the OPPOSITE side ( make sure you keep away from open flame or spark and wear appropriate clothes and eye protection. SAFETY FIRST!) then you clear out whatever is inside the air filter housing by using compressed air or a damp clean lint free cloth. After you are done with that, remove the spark plug, check for broken or worn out plug if carbon deposits are present, clean it with a wire brush and re-gap it using a spark plug gap tool and adjusting it according to specs. Worse case scenario is to replace the plug with the appropriate number and reinstall. The carburetor on the other hand requires a little more attention to detail, first thing you should know is that gasoline after sitting for a while decomposes as it has a distinct smell and gums up the orifices in the carburetor. First thing you do is perform your visual inspection just as before, then inspect it for leaks from the float bowl gasket and surrounding area. Then you must take the carburetor apart taking note of all the pieces removed, take it step by step and take pictures if you can.. (don't rush it !). Pick up some de-carbonizer spray from your local auto parts store and clean the carburetor inside out THOROUGHLY especially the inner port holes. Replace all gaskets with a gasket kit supplied by Briggs manufacturer and reassemble according to spec sheet. Reinstall the carburetor and fire it up making adjustments to the idle, and mixture settings screws located on the bottom or side of carburetor. If everything is done correctly you should have a rebuilt carb ready for action.
I hope this helps. Good Luck.
 

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Discussion Starter · #3 ·
Re: 4HP Briggs - Rich mixture

Thanks alot, my mower runs like it's brand new!

However, I did opt for the sure thing any replace the carburetor. The price was right at $25:). although I am sure replacing the diaphragm, gasket and a thorough cleaning as you suggested would have accomplished the same.
 
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