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  1. #1
    Sawfxr's Avatar
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    6.75 Briggs Auto choke

    I'm helping a co-worker with a newer Toro that has the air vane operated auto choke. It also has the bi-metal arm that's supposed to hold the choke off while starting the engine when it's already hot. This mower had a huge mouse nest under the flywheel housing and the owner removed it himself. Since then the engine surges bad as the air vane arm keeps moving the choke lever on and off.
    I can't figure out how or if the bi-metal arm connects to the air vane. I'm thinking there was a second spring that got unknowingly removed with the mouse nest debris. Is there supposed to be another spring connecting the two parts? Do the two arms directly hook together? Or does the bi-metal arm just act as a limiter to the movement of the air vane arm?
    Thanks in advance for all and any replies.
    E.
    Nothing runs like a Deere


    Dedicated to those that simply went to work on a Tuesday morning. 9-11-01

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  3. #2

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    Re: 6.75 Briggs Auto choke

    There is NO second spring. If the bimetallic choke arm is set properly the cause of the problem is probably dirt in the carb main jet. These carbs are very sensitive to dirt.

  4. #3
    pugaltitude's Avatar
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    Re: 6.75 Briggs Auto choke

    There should be a spring connected from the choke lever on top of carb to a metal cover with a little
    hook cut out where the carb fits to engine.
    The thermostat (bi metal arm) is common for seizing and sticking which can keep choke on causing rough running and bad starting.
    Model,type and code should help to identify spring.
    The "best" engine you will ever own!

    Briggs & Stratton MST.

  5. #4
    Sawfxr's Avatar
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    Cool Re: 6.75 Briggs Auto choke

    Hey, Thanks for the replies.
    The bi-metal arm appears to be doing it's thing as it does move back and forth when heating up and cooling down. I just was not sure if there was a second spring used to connect it or not . I did figure out that the hook at the end of the air vane did belong around the bi-metal arm and not in front of it as I found it. Now that I'm sure it's together correctly I hoped the hard starting when hot would be gone. It is still a problem. As far as the surging, I have soaked the carb twice now for a total of about 2 hours and it still surges. If I hold the choke partially closed with my finger it smooths right out so I'm sure its a carb issue still. My next thought is for $35 I can replace the carb with a primer type carb and change the air filter base to the primer type for an additional $18. I have another similar mower with the primer setup (no choke plate) and it starts every time when hot with one pull. A new primer carb should kill both problems ;>)
    Thanks.
    E.
    Nothing runs like a Deere


    Dedicated to those that simply went to work on a Tuesday morning. 9-11-01

  6. #5

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    Re: 6.75 Briggs Auto choke

    Just remember something after I saw your post. I think that there is a replacement carb to be used on engines with your problem. Ask your B&S dealer if they have service bulletin #760. Why I can remember that number I don't know. If they do ask them to see if the recommended carb has been superseded to a different number. I will try to remember to look for this SB when I go in to work Monday, but my short term memory has gone the way of the two cycle engines, so it may take some time to find it.

  7. #6
    pugaltitude's Avatar
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    Re: 6.75 Briggs Auto choke

    Briggs ready start has had cold and hot start problems over the years.
    The thermostat has to be set up correctly. on the plastic air vane near the thermostat there are 4 adjustment lugs. Bend the top of the thermostat so it aligns in between the lugs with forward to back and side to side adjustment.
    Also depending on the manufacture date depends on the spark plug gap. Need model type and code to give you that info.
    Also does it have a metal spark plug cover. They prone to causing no spark when hot.
    Governor spring can also be updated to stronger spring from the older quantums.
    If all else fails try a carb part no 794304 which now has an idle circuit built in to help start.
    Good luck.
    The "best" engine you will ever own!

    Briggs & Stratton MST.

  8. #7
    Sawfxr's Avatar
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    Question Re: 6.75 Briggs Auto choke

    Thanks again for the replies.
    pugaltitude,
    Do you have a page from the service manual detailing the adjustment of the thermostat?
    The numbers on this engine are 126T05 / 0123-B1. No metal spark plug cover.
    I had a mower in the garage with the primer system on the B&S engine. Since that mowers carb was already off, just for kicks I switched the carbs and this problem mower starts when hot with no hesitation. We were about to pull the trigger on ordering the primer carb and air filter base later today.
    Thanks
    E.
    Nothing runs like a Deere


    Dedicated to those that simply went to work on a Tuesday morning. 9-11-01

  9. #8

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    Re: 6.75 Briggs Auto choke

    This auto choke is so new that it is not in the service manual yet. I forgot to grab the instruction sheet at work today. I will try to remember tomorrow.

  10. #9
    Sawfxr's Avatar
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    Question Re: 6.75 Briggs Auto choke

    OK. We did the carb swap to the primer style and she starts like new hot or cold. One pull.
    But... it still surges up and down.
    I sprayed carb cleaner around everything looking for an air leak but didn't find one. It will stop surging if I hold the throttle shaft steady with my finger, then let go and it will stay smooth. Do a little bit of cutting heavy grass and once the governor moves the throttle then it's back to constant surging until I touch the throttle shaft again.
    I'm wondering if it could be valve related??
    Thanks.
    E.
    Nothing runs like a Deere


    Dedicated to those that simply went to work on a Tuesday morning. 9-11-01

  11. #10

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    Re: 6.75 Briggs Auto choke

    Main jet needs cleaning.

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