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    needsinfo44's Avatar
    needsinfo44 Posts: 4, Reputation: 1
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    #1

    Jul 22, 2009, 02:09 PM
    12.5 HP Briggs engine runs to fast.
    My ridding mower engine starts fine but runs estremely fast and I can't slow it down. Governor seems to be working as arm moves on start up and stays there. Turned fuel, air mixture closed with no slow down from engine. Any ideas??
    needsinfo44
    KISS's Avatar
    KISS Posts: 12,510, Reputation: 839
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    #2

    Jul 22, 2009, 02:16 PM

    Spray carb cleaner at the part the governor moves on the carb. It has to move very freely.
    needsinfo44's Avatar
    needsinfo44 Posts: 4, Reputation: 1
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    #3

    Jul 22, 2009, 02:37 PM

    The governor is not sticking, it move freely,back and forth. I can push it back to its before starting position and engine still runs fast.
    needsinfo44
    crigby's Avatar
    crigby Posts: 4,343, Reputation: 107
    Outdoor Power Equipment Expert
    		  
    #4

    Jul 22, 2009, 02:57 PM

    Hi,
    Sounds as if the throttle shaft has broken in two. It usually does it at the screw the holds the throotle plate. No way for it to shut. If you reach above the carg and try to lift it ; it should move upward until it touches the base of the air cleaner. Seen it more on Kohler Commands than Briggs, and fairly rare.
    Peace,
    Clarke
    needsinfo44's Avatar
    needsinfo44 Posts: 4, Reputation: 1
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    #5

    Jul 25, 2009, 05:31 PM

    Crigby: Throttle shaft is not broken, but I am puzzeled about the throttle linkage. The linkage does activate the choke, but will not slow down the engine. Maybe I just need a new carburetor? Thanks Needsinfo44
    KISS's Avatar
    KISS Posts: 12,510, Reputation: 839
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    #6

    Jul 25, 2009, 06:04 PM

    Manually move the governor linkage. A spring could be missing too.

    Use either Home - Briggs & Stratton or Parts & Accessories | Shop & Find Lawn & Garden, Appliance Parts at Sears PartsDirect | SearsPartsDirect.com for a linkage diagram.

    Two things come to mind:
    1) spring
    2) Throttle plate is stuck.
    crigby's Avatar
    crigby Posts: 4,343, Reputation: 107
    Outdoor Power Equipment Expert
    		  
    #7

    Jul 25, 2009, 07:36 PM

    Hi,
    Well, the throttle shaft was a long shot with a Briggs, happens to Kohler Command singles.
    Let us try the governor adjustment. Put the throttle in the full open position (not choke) and usng a 3/8" wrench loosen the pinch nut at the bottom of the governor lever. The shaft usually has a small hole through which you can insert a small drill bit or such (I use a small Allen wrench) and turn the shaft clockwise as far as possible (should not be much, but it sounds like it may be a bit.) Now carefully tighten the nut taking care not to change the relationship between the shafr and lever.
    Now try again. Hopefully the governor itself is not out, far rarer than it was 25 years ago.
    Peace,
    Clarke
    gotalk's Avatar
    gotalk Posts: 3, Reputation: 1
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    #8

    Jun 22, 2011, 04:22 PM
    Hey needsinfo44, I know it's a long shot to think that you would still look at this, but it sounds exactly like the problem I'm having (and just posted) with my 12.5 hp briggs. Did you ever figure out the problem?
    needsinfo44's Avatar
    needsinfo44 Posts: 4, Reputation: 1
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    #9

    Jun 23, 2011, 10:39 PM
    I looked at this Sears 12.5 hp mower again and finally figured out the problem. The baffle plate fell off the shaft so the governor couldn't work. I assume the small screws that held the baffle to the shaft were swallowed by the engin. Don't know about any damage without tearing the engin down. I put the baffle plate back together and am trying to get this engin to run properly again. This was a really weard happening and I have bought a bigger mower, but kept the old one around as I was determined to figure it out. I just gave it one last try and found the problem. A good answer to remember. NEEDSINFO44
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