The carburetor must vaporize the fuel and mix it with

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Unformatted text preview: uid” gasoline. The carburetor must vaporize the fuel and mix it with air in the proper proportion. A carburetor is a device that is operated by pressure differences. The downward movement of the piston creates a partial vacuum in the cylinder. As soon as the intake valve opens atmospheric pressure forces air through the carburetor and manifold to fill that vacuum. The carburetor creates a partial vacuum of its own by means of a venturi for the purposes of drawing fuel into the air stream. A venturi is a restriction in a passage, which causes air to move faster. When the fuel moves into the intake manifold (which is under partial vacuum), the boiling point of the gasoline is lowered. This causes many of the atomized particles to “boil” or “flash” into a vapor. Partially vaporized fuel moves through the manifold. The heat of the manifold walls warms the fuel. This causes further vaporization. When the mixture enters the combustion chamber, both the swirling motion and sudden increase in temperature due to the compression stroke completes the vaporization of the fuel. Natural draft carburetor (cross draft) Float type fuel supply The purpose of the carburetor float is to maintain a constant level of fuel in the float bowl. The float rises and falls with the fuel level. As fuel is used from the float bowl, the float lowers and unseats a needle valve, which lets fuel enter the bowl. This in turn raises the float, seating the needle and shutting off fuel supply to the bowl. Faculty of Engineering & Applied Science Memorial University of Newfoundland ENGI 1030 Lawnmower Disassembly/Assembly General Disassembly Instructions 1 Disconnect spark plug wire. Remove spark plug. 2 Remove starter assembly from engine shroud. 3 Remove fuel clamps. Disconnect fuel supply hose. Be careful not to spill fuel. Remove fuel tank. 4 Remove air intake/filter. 5 Remove engine shroud. 6 Remove cylinder head. (Careful with the gasket). Turn flywheel to observe operation of valves. 7 Disconnect and remove the...
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