Briggs & Stratton 276535, Repair Manual

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2-Cycle Snow Engine
Section 1 - General Information
Page 1
SECTION 1
GENERAL INFORMATION
TWO-CYCLE ENGINE THEORY
In a piston-ported engine, the fuel mixture enters the
crankcase through a port that comes directly from the
carburetor (commonly referred to as a “third port”), See
item
figure 1.
Fig. 1
At about 28° before top-dead-center (BTDC), the spark
plug ignites and forces the piston away from the spark
plug. As the piston moves away from the spark plug, it
exposes the exhaust port (Item
Figure 2) and the
expanding exhaust gases escape. As the piston
continues to move away from the spark plug, it
compresses the fuel mixture (Item Figure 2) that is on
the bottom side of the piston in the crankcase.
Fig. 2
Near the bottom of its travel, the piston uncovers the
pressure transfer port and allows this compressed fuel/
air mixture to expand into the combustion chamber
(Item
Figure 3).
Fig. 3
Now the piston begins its travel in the opposite direction
and first closes off the transfer port and then the exhaust
Intake Ports Closed
Ignition
Third Port Open
Partial Vacuum
Intake Ports Closed
Exhaust Port Opening
Third Port Closed
Pressure Building Up
Intake Ports Open
Exhaust Port Open
Fresh Fuel Change
Third Port Closed