Suitable Replacement Stihl 031AV Carburetor Parts
The Stihl 031AV carburetor has two different sides. First, the fuel pump side of the carburetor pumps fuel from the fuel tank through the fuel line to the metering side of the carburetor. Second, the metering side of the carburetor supplies fuel to the jets in the carburetor so the saw idles properly. Additionally, this side allows the saw to accelerate to full throttle instantly when the throttle is activated [pulled]. Finally, this side maintains fuel to the chain saw motor at full throttle regardless of the position of the saw.
The carburetor has diaphragms and
gaskets to help it pump and meter the fuel by crankcase impulse.
Every time the piston goes up and down, it creates vacuum and
pressure in the crankcase. The Stihl 031AV carburetor uses this pulse via a
pulse line connected to the crankcase or through the carburetor
intake to get the pulse needed to properly make the carburetor
On the metering lever side of the Stihl 031AV carburetor, there is a diaphragm and gasket with a cover plate
screwed to the carburetor. The metering diaphragm controls the
amount of fuel allowed to enter the metering lever side of the
carburetor. The diaphragm is either connected or just touching the
fulcrum [meter lever] and when fuel exits the metering side of the
carburetor through the jets in the carburetor, atmosphere pressure
[14.7 psi] pushes the diaphragm in letting more fuel in. As the fuel
rises to fill the metering lever side of the carburetor, the inlet
needle valve closes the fuel off from the fuel pump side of the
carburetor. The needle valve goes into the body of the Stihl 031AV carburetor and
is fastened to the metering lever fulcrum which has a spring under
the opposite side of the needle valve to keep pressure on the needle
valve when closed.
On the metering lever side of the Stihl 031AV chainsaw carburetor there are two sides, a low side and a high side. The low
side controls idle and acceleration when the saw starts to rev up.
The high side controls the amount of fuel the saw will receive at
full RPM. Some carburetors will have 2 adjusting screws, one for the
low side and one for the high side. There is also an idle screw
which makes contact with the throttle shaft to control idle speed
along with the low side of the carburetor. Note that some chainsaw model carburetors
have just one adjusting screw and the other side is prefixed and
non-adjustable. Some may also have no adjusting screws [except the
idle screw] to preset or pre-jet the carburetor.
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