How does fuel stop when carb float rises?


Old 07-13-14, 05:31 PM
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How does fuel stop when carb float rises?

So, I get the principle that the carb float acts like a toilet float but when it blocks the inflow of fuel, the... the fuel pump is still going so why doesn't fuel pour out of the pipes or pump?
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Old 07-13-14, 05:45 PM
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Hello qwertyjjj,

Simple, The pressure/tension the float puts on the needle valve to stop the fuel from flowing is greater than the fuel pumping pressure......

Old 07-14-14, 06:38 AM
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And to elaborate a bit more... The float is rather large so it can exert a pretty decent up force. The float is also mounted at the end of the float arm while the needle valve is located very near the pivot point. This provides a lot of mechanical advantage. And lastly, the needle valve has a very small surface area. Even high pressure fuel acting on such a small surface (hydraulics) can not exert much force so it's relatively easy for the needle to remain sealed against the pressure.

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