How Things Work How-Carburetors-Work

Published on October 15th, 2015 | by Kimberly Myers


How Small Engine Carburetors Work

What is a carburetor?

A carburetor is the device(?)  inside an internal combustion engine that provides the area for air and gasoline to mix together


  • Float pin
  • Float bowl
  • Venturi
  • Choke valve
  • Throttle valve
  • Needle
  • Main jet
  • Idle jet


How a carburetor works:

  • Air enters the carburetor through the engines air intake system
  • How much air enters the carburetor depends on the setting of the choke, which covers the valve the more open the choke is, the more air can enter
  • The air is pushed through an opening that narrows called the venturi.
  • This creates a vacuum that pulls fuel in through the very small fuel jet, which lets just enough fuel in to create the right ratio for an explosion to power the engine
  • Extra gas is held in the float bowl, when the bowl is full the float “floats” to the top and closes off the area that the fuel flows through,
  • as the gas is released into the chamber, the float falls with the level of the gas and un-blocks the chamber opening, allowing the fuel bowl to fill back up
  • When the throttle valve is open, gas is released more rapidly to make sure there is enough power to make the equipment go faster.
  • When the throttle is closed and the engine is idling, there is a secondary valve called the idle valve on the outside of the throttle valve

Maintenance tips:


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3 Responses to How Small Engine Carburetors Work

  1. kermit vetter says:

    Briggs & Stratton engine Model 12H802 Carburetor needle & seat P/N 398188 can anyone tell which way the Neoprene seat goes into the Carb? Grooved side towards the needle or the other way around? I ought the kit from Jack’s but I have no instructions as to which way it goes seat goes in.

  2. Patrick Vicks says:

    how do i get the carberator off of briggs and straton lawn mower. I took all of the screws off and still can’t get it off.

  3. Have a Yardman grass trimmer.. engine will start but then just stops like iike it runs out of gas. I have checked the gas lines.. all clear, good flow, have removed the Zama carburetor and cleaned with cleaner and blew out with air.. still wont continue to run.. whats going on?

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