My car is a 1987 Toyota Tercel DX Wagon 1452cc 2bl manual driven car. Carburetor of it is a Aisan 14120 Two Barrel carburetor.

I have removed the carburetor of my car for repair. I know all the components and their functions, except this one.

this one.

That part has a one orifice for the secondary barrel throat. Other end goes to the intake manifold.

This is not for the Secondary Throttle Diaphragm. It connects to an other place.

This chamber is covered with a plate with a gasket. Inside this small chamber, there is a plate like valve.


I couldn't find this in any carb manual.

Please tell me What is this part and what is the function of it?

2 Answers 2


Hot Idle Compensator Valve (HIC)

After Googling for long period, I found this as a place for Thermostatic valve named "Hot Idle Compensator" Valve.

As described in this link,

High air temperature at carburetor inlet causes gasoline to evaporate rapidly, which intern can produce highly rich idle mixture. In order to overcome this problem, many carburetors use a hot idle compensator valve, which is a thermo­static valve consisting of a bimetal spring, a bracket, and a small poppet. The compensator valve is usually located either in the carburetor barrel or in a chamber on the rear the of carburetor bowl. A dust cover is placed over the chamber. The hot-idle compensator valve is normally closed by spring tension and engine vacuum. As temperature rises, the bimetal strip bends. This uncovers an auxiliary air passage, or air bleed, through which air enters the carburetor below the throttle plate. As this extra air mixes with excess fuel to lean out the idle mixture, it prevents stalling and rough idling. Once the carburetor temperature returns to normal, the compensator valve closes to shut off the extra air supply.




It looks to me like an acceleration valve.

When driving normally or accelerating gently, the valve remains closed. This, of course, minimises fuel consumption. The car is running using just one barrel of the carburettor.

If you accelerate hard, the vacuum increases, which opens this valve. The second barrel starts to supply fuel and the car will accelerate more enthusiastically.

This is separate to the throttle butterfly on the second barrel which still controls the fuel flow once the acceleration valve is open.

I can't speak for the specific carburettor in your pictures but I've seen similar valves on various cars.

  • Thanks @Chenmunka. But there isn't any way to fuel to be mixed. This starts from the very beginning of the secondary barrel. Venturi lies below to this. Also there isn't any Pump Jet (which add fuel at the very beginning) for the secondary barrel. So this bypass the fuel mixing places (Venturi and Throttle)
    – user31310
    Commented Jul 31, 2017 at 8:34

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