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NotTaR of small Gasoline Engines and Rotary Lawn Mowers : Basic operation of a float type carburet..  
 Copyright © 1994-2007, Samuel M. Goldwasser. All Rights Reserved. Reproduction of this document in whole or in part is permitted if both of the following conditions are satisfied: 1. This notice is included in its entirety at the beginning. 2. There is no charge except to cover the costs of copying. I may be contacted via the Sci.Electronics.Repair FAQ (www.repairfaq.org) Email Links Page.

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Basic operation of a float type carburetor

The diagram below shows a schematic of a typical float type carburetor with the engine running at high speed. The choke plate is fully open and the throttle plate is opened the proper amount be feedback from the governor to maintain the speed set by the user throttle control.


            Air filter       (Air: -->, Air+fuel: ==>)
          _____________
         /             \  Choke plate               Throttle plate
          | ||||||||| |  (Fully open) Venturi      (Partially open)  
          | ||||||||| |______________    v   _______________________________
          | |||||||||                \______/
          | ||||||||| -> -> -> -> ->           ==> ==>      /  ==>  Intake
          | ||||||||| ->  ----O----  ---> ===> ==> ==>    O    ==>  pipe to 
          |           -> -> -> -> ->  __||__   ==> ==>  / |    ==>  cylinder
           \____________________  ___/  ||  \_____________|__________________
                                ||      ||                |
    Fuel __________ Air bleed ->||      ||<- Main nozzle  o---------+ 
   Inlet ______    |____________||______||__                        |--> Pull
            |  |_ _|                    ||  \       Speed <--/\/\/--+    from
   Needle ->|  __A_______________       ||   |     control   Spring    governor
   Valve    | |o__/              \      ||   |                          closes
            |-----|     Float     |-----||---|                         throttle
            | . . |               | Gas || . |<- Float bowl              plate
            | . . .\_____________/. . . || . |
             \______________________________/
                                         

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