Diaphragm on side of TK Carb
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Thread: Diaphragm on side of TK Carb

  1. #1
    Junior Member GNolan's Avatar
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    Feb 2019
    Clarkston MI

    Diaphragm on side of TK Carb

    Hello Everyone,

    Can anyone tell me what the Diaphragm does on the TK Carb? Theory and/or purpose of it and how it works? I know it is the fuel shut off or something like that and vacuum operated. It opens and closes a valve or bypass of sorts. Please educate me to understand how this operates.

    Thanks, Greg Nolan

  2. #2
    Senior Member RockyTFS's Avatar
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    Feb 2011
    Hailey, ID
    I wondered too. I found this:

    COASTING ENRICHER - Feeding a Closed Mouth

    You're blasting down the trail and you see a hairpin coming up, so you close the throttle. This closes the butterfly valve. You and your 400lb baby (the bike, not the other love of your life), are still rolling with inertia, keeping the engine revs high. Now it can't get the mixture it's trying to suck in because the butterfly valve is closed, blocking the air flow. To compensate for this there's an air jet in the lower diaphragm chamber that transfers ambient pressure to one side of the coasting enricher's spring loaded cut off valve. The excess vacuum in front of the butterfly valve is transferred to a drilling that leads to the other side of the cut off valve. This sucks it open, allowing the pilot jet to feed more fuel to the engine preventing an overly lean condition. (Pop. Pop. Pop.)

    This isn't a TK carb, but the principle is the same.
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  3. #3
    Senior Member jbfla's Avatar
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    Jul 2010
    FL. GA, NC
    Thanks, Rocky.
    Best explanation I have seen.

    Here are the corresponding inlet holes on the TK cv carb:

    Last edited by jbfla; 05-14-2019 at 03:16 PM.
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  5. #4
    Senior Member GaryL's Avatar
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    Jun 2013
    Forestburgh, NY
    Good explanation however Gnolan has an old style TK carb that does not have the flap. I call this diaphragm a deceleration circuit that probably performs the same function but in the old style carbs it works a little different. I know when this system is not functioning properly the bike will back fire on deceleration which probably indicates the carb is getting too much fuel when none is being called for.

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