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Briggs And Stratton Carburetor Settings

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#1 MR Simplicity 6111 OFFLINE  

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Posted October 29, 2012 - 11:51 AM

I have a 12hp B+S engine but i think the the mixture. etc screw are messed up. Does anyone now the settings for the screws( see picture). | am wondering about the screw on the bottom of the float chamber and the one directly below the air filter. Any help would be appreciated.

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#2 HDWildBill ONLINE  


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Posted October 29, 2012 - 12:40 PM

What makes you think they are messed up? I usually set the screw to 1 1/2 turns to start with then let the engine warm up and move it to full throttle. Then adjust the bottom screw (high speed) until the engine smooths out and I get the highest RPM then I will turn the screw in an 1/8 - 1/4 turn to lean it a bit. Them pull back to Idle and do the same with the idle screw (Low speed) then adjust the idle screw.
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#3 Bruce Dorsi OFFLINE  

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Posted October 29, 2012 - 12:46 PM

Final adjustments to the mixture screws is always done when the engine is running and warmed-up.

GENTLY turn both mixture screws clockwise until movement stops. ...Excessive force can damage the tips of the adjustment needles.

The initial adjustments for your "large one-piece Flo-Jet carburetor" are 1-1/2 turns out (counterclockwise) from the closed position. .....These adjustments are usually "close enough" to get the engine started if you do not have other problems.

The small adjuster below the air cleaner is for idle mixture. ....The adjuster at the bottom of the float bowl is the high-speed mixture adjustment.

(1) Start the engine and allow it to run a few minutes to warm up.

(2) Set the throttle to the FAST position, but make certain the choke is not being activated (closed partially).

(3) Turn the main adjuster (bottom of bowl) clockwise until you notice engine speed drops slightly.

(4) Then turn the main adjuster counter-clockwise slightly to "richen" the mixture. .....Black smoke or rough running indicates a too-rich mixture.

(5) With the throttle moved to the SLOW position, the speed adjusting screw should be against the throttle stop. .....The idle speed should be approx 1750 rpm for aluminum engines or 1200 rpm for cast-iron engines. ....If the idle speed needs to be adjusted, the speed adjusting screw can be turned clockwise to increase the speed, or counterclockwise to lower the idle speed. [You may need to manually rotate the throttle so the screw contacts the stop, while you make a speed adjustment.]

(6) Now, with the throttle held against the stop, adjust the small idle mixture screw under the air cleaner to obtain a smooth idle.

(7) If the engine stumbles when accelerating from idle to high-speed, or under load, the high-speed adjuster under the carb bowl can be turned counterclockwise slightly to richen the mixture.

On some mowers and tractors it may be necessary to adjust the mixture while the blades are turning to increase the load on the engine. .....If you do this, BE CAREFUL and STAY AWAY FROM THE SPINNING BLADE(S) !!!!!!!
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#4 Farmlife OFFLINE  


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Posted October 29, 2012 - 04:54 PM

Great info here guys. Seems so simple but many overlook these simple steps.
  • MR Simplicity 6111 said thank you