Section 4 Air Intake And Exhaust System - ZONGSHEN ZS125-86 Service Manual

The induction system of the motorcycle engine is composed of air cleaner, intake pipe and so on. The
main function of the induction system is to guide and filter the air, reduce the noise and control the amount
of the gas mixture into the engine.
The exhaust system mainly consists of a exhaust pipe and a silencer. The main function of the
exhaust system is to remove the exhaust gas from the engine to the atmosphere, reduce the noise and
exhaust gas temperature during the exhaust, and eliminate the flames and sparks in the exhaust gas. A
good exhaust system can also improve the induction and exhaust efficiency, increase the engine power,
and reduce fuel consumption, etc. The exhaust system including an exhaust pipe and a muffler is known
as the exhaust silencer.
1. Structure and Working Principles of Induction System
[1]Structure and Working Principles of Air Cleaner
The air cleaner is an important part of the induction system. It filters and purifies the air into the
cylinder, prevents dust, sand and other particulars in the air from entering the cylinder, and reduces the
abrasion of cylinder, piston and piston ring. Its work performance has a great influence on the engine's
power performance, induction noise and service life. Experiments show that the absence of air cleaner will
cause the cylinder subjected to 8 times increase the abrasion loss, the piston to 3 times and the piston
ring to 9 times, greatly reducing the reliability of the engine and shortening its service life. Therefore, the
motorcycle must be equipped with an air cleaner. Under the premise of satisfactory filtering effect, the air
cleaner is required to impose low airflow resistance, so as to improve the intake by the engine. Besides,
the air cleaner is also required to be reliable in operation, simple in structure, small in size, light in weight
and easy for maintenance. An air cleaner mainly includes a filter element and a shell of airtightness and so
on. When the engine is running, the air enters the front chamber of the air cleaner via the air duct, passes
through the filter element and flows into the rear chamber of the air cleaner, and then enters the throttle
valve.
[2.]Structure and Working Principles of Intake Pipe
The intake pipe is an important part that connects the throttle valve to the engine inlet, and also
supports the function of the throttle valve. It is simple in structure. Its curved shape mainly depends on
2. Structure and Working Principles of
Exhaust System

Section 4 Air Intake and Exhaust System

the relative locations of the throttle valve and the
engine inlet, but also considers the impact on
intake resistance. A long airway is conducive to
fuel atomization, but subject to higher airflow
resistance; a short airway is disadvantageous
to fuel atomization, but subject to lower airflow
resistance.
The gas mixture atomized by the injector enters
the engine cylinder via the engine inlet and through
the intake pipe. The intake pipe reduces the heat
transferred from the engine to the throttle valve
and isolates the impact of engine vibration on the
throttle valve.
The exhaust pipe in the exhaust muffler is
made of a bent steel pipe. Located between the
engine outlet and the silencer, It serves to direct the
exhaust gas from the engine to the silencer.
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