Carby NT carb question

dougsr.874

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Sep 15, 2008
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Right or wrong the easiest way I've found to start a Chinese 2 stroke is to hold the primer valve down on the carb till a few drops of gas come from the throat of the carb....that way you never have to use your 3rd hand to work the choke.....NOW THE QUESTION: The last two carbs I've had will not allow the gas to flow out the throat of the carb. with the primer valve depressed......The only thing I can figure is that the primer valve is too short to hold the float down far enough.. any comments ??????
 


Skyliner70cc

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So you are clogging your airfilter with residual oil in the fuel mixture?

The primer button works great, all you have to do is press it while your roll throttle to full throttle.
 

Skyliner70cc

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Flooding a carb/engine is not a good idea. THe primer button is designed to refill the carburetor float bowl but not to the point it is leaking out of your carburetor.
 

sp454e

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Flooding a carb/engine is not a good idea. THe primer button is designed to refill the carburetor float bowl but not to the point it is leaking out of your carburetor.
now i understand more about primer Q. I have fuel coming out of the primer button, does the float level have something to with this.
 

Skyliner70cc

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now i understand more about primer Q. I have fuel coming out of the primer button, does the float level have something to with this.
Quite possibly your float is not setup correctly causing it to overfill. Also, double check the primer button area as not unusual for it to fail or have a missing or poorly sealing gasket. If my bike has not been run for a week, 3 pushes on the primer with about 1/2 to 3/4 choke is all is needed for engine to fire instantly.
 

motorpsycho

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Wrong.
when you push the primer button, its designed to push the float down, which opens the needle & seat. this allows more gas to flow into the already full float bowl. when you release the primer button, the float rises & closed the needle & seat. where do you think that extra fuel goes that you let into the float bowl by pumping the primer button?
That extra fuel will come up through the main jet & into the carb, which is why the engine is easier to start. it would be the dame as if you squirted a little gas .into the back of the carb
I have a 66 triumph Bonneville with twin amal carbs on it & they both have primer buttons. (Or ticklers as they are called) so I know how they work.the same thing happens when you pump the primer bulb on your weedeater carb. the pressure from the bulb forces fuel into the carb, last the needle & seat and into the carb throat.
neither if these were designed to literally flood the engine. they just allow enough fuel into the carb for easier starting.
 
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Skyliner70cc

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If your float not setup correctly, it is possible for the needle to be open and not close when float bowl is full. It is also possible for float twangs not allow enough fuel flow into bowl when bowl is pressed down by primer or when on bottom of dry bowl.

A propertly setup carb should not even need a primer button to refill float, it should be automatic when bowl is dry and needle is opened already to allow fuel flow. In my opinion, the primer works more by allowing displaced air to evacuate the float bowl faster by going past the primer button allowing faster fuel fill then just pressing the float down....a dry float bowl will already have the float in down position.

You can double check my theory by draining float bowl with drain screw (fuel petcock and lines free of fuel), open fuel petcock valve and see how much fuel comes out of the dry float bowl (remember, float is already on bottom and needle valve should be open for fuel to flow). Press primer button about 1/2 way which won't touch float or push it down further (remember, in dry bowl, float is sitting on bottom) but is enough to break airseal and watch the fuel flow rate...should be greater than before.
 
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