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How does fuel stop when carb float rises?

qwertyjjj's Avatar

Join Date: Jun 2014
Posts: 1,156

07-13-14, 05:31 PM   #1  
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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31YTech's Avatar

Join Date: Feb 2008
Posts: 1,263

07-13-14, 05:45 PM   #2  
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......


Pilot Dane's Avatar
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Join Date: Mar 2003
Posts: 16,684

07-14-14, 06:38 AM   #3  
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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