1. Fuel System
The fuel system supplies the air and fuel necessary for an engine to produce power.
The fuel system includes:
Air Cleaner Fuel Supply Carburetor Governor
Functions of the Air Cleaner
1. Removes dirt and dust from air before it enters the engine.
2. Helps quiet the rush of air into the engine.
3. Prevents fire in the event of an engine "backfire".

2. 3 Functions of the Air Cleaner
1. Removes dirt and dust from air before it enters the engine.
2. Helps quiet the rush of air into the engine.
3. Prevents fire in the event of an engine "backfire".

3. Types of Air Cleaners
1. Dry Element:
Made of a filter paper which traps dirt as the air passes through it.
2. Oil Bath:
This type of cleaner consists of a bowl, screen, and an oil supply. Air enters the cleaner through the top and moves down into the oil bath at the bottom of the cleaner. As the air passes through the oil dirt particles become coated with oil. As the air passes through the wire mesh, dirt particles stick to the mesh and the cleaned air continues on into the engine.

4. 2. Oil Bath:
This type of cleaner consists of a bowl, screen, and an oil supply. Air enters the cleaner through the top and moves down into the oil bath at the bottom of the cleaner.
As the air passes through the oil dirt particles become coated with oil. As the air passes through the wire mesh, dirt particles stick to the mesh and the cleaned air continues on into the engine.

6. Fuel System
Oil Foam:
Consists of a foam material soaked with oil. As dirty air moves through the foam dirt particles become trapped. The cleaned air continues on into the engine.

7. Fuel Supply
The fuel supply provides passage of the fuel to the carburetor
Three Types of Fuel Supply
Gravity Feed
Engines using this supply system must have the fuel tank located higher than the carburetor.
Gravity allows the fuel to move from the tank to the carb. A fuel valve is used to turn the fuel on/off.

9. Three Types of Fuel Supply cont…
2. Vacuum Feed
In a vacuum feed system the fuel tank must be placed directly underneath the carburetor. As the piston moves down the cylinder the vacuum created pulls fuel through the fuel line into the carb.

11. Three Types of Fuel Supply cont… 3. Pressure Feed
This system relies on a small fuel pump to move the fuel from the tank to the carb. Because this is a pressure system the fuel tank can be located some distance from the engine.

13. Fuel System Carburetors
Purpose of the Carburetor is to mix air and fuel to permit proper operation of the engine.
Major Parts of the Carburetor
Needle Valve: small valve located in the carb. which regulates the flow of fuel.

14. Float: A hollow container connected to the needle valve which maintains a constant fuel level.

15. Diaphragm: A small piece of flexible metal which replaces the float in some types of carburetors

16. Venturi: A restriction in the intake manifold.

17. Intake Manifold: Part of the engine which connects the carburetor to the combustion chamber.

18. Choke Plate:
A small disk located inside the carburetor which is used to assist the starting of an engine.
The choke restricts the flow of air into the engine allowing more fuel to enter for easier starting.

19. Throttle Plate:
Controls the flow of fuel and air into the engine.
By controlling the flow of fuel we can control the speed of operation of the engine.
Fuel Nozzle:
A very small opening in the venturi leading from the fuel tank or bowl through which gasoline enters the intake manifold.

20. Main Fuel Adjustment Screw
A type of needle valve which controls the mix of air and fuel recommended for proper operation of the engine at normal operating speeds.
Idle Fuel Adjustment Screw
A needle valve which controls the mix of air and fuel when the engine is at idle speed.

21. Fuel System: Types Of Carburetors
Float Carburetors This type of carburetor uses a small metal or cork float to maintain a constant fuel supply.

22. Fuel System: Types Of Carburetors
Float Carburetors This type of carburetor uses a small metal or cork float to maintain a constant fuel supply. The float is connected to a needle valve which permits fuel to enter the bowl.

23. Fuel System: Types Of Carburetors
Float Carburetors This type of carburetor uses a small metal or cork float to maintain a constant fuel supply. The float is connected to a needle valve which permits fuel to enter the bowl. When the engine is started the piston moves downward and fuel is drawn out of the bowl causing the float to drop, opening the fuel inlet valve.

24. Fuel System: Types Of Carburetors
Float Carburetors( Con’t) Fuel enters the bowl at a rate equal to the amount being used by the engine.

25. Fuel System: Types Of Carburetors
Float Carburetors( Con’t) Fuel enters the bowl at a rate equal to the amount being used by the engine. When the engine is stopped the bowl fills with fuel raising the float and closing the inlet valve stopping the flow of gasoline.

26. Fuel System: Types Of Carburetors
Vacuum Feed Carburetors This type of carburetor requires the fuel tank be placed directly underneath the carburetor.

27. Fuel System: Types Of Carburetors
Vacuum Feed Carburetors This type of carburetor requires the fuel tank be placed directly underneath the carburetor. A short fuel line connects the venturi of the carburetor to the fuel tank.

28. Fuel System: Types Of Carburetors
Vacuum Feed Carburetors This type of carburetor requires the fuel tank be placed directly underneath the carburetor. A short fuel line connects the venturi of the carburetor to the fuel tank. When the piston moves down the cylinder air is 'sucked' into the engine.

29. Fuel System: Types Of Carburetors
Vacuum Feed Carburetors (Con’t) As the air moves into the engine through the intake manifold fuel is drawn up the small fuel line and mixes with the rushing air.

30. Fuel System: Types Of Carburetors
Diaphragm Carburetor Diaphragm carburetors maintain a constant fuel supply by means of a flexible metal disk called a diaphragm.

31. Fuel System: Types Of Carburetors
Diaphragm Carburetor (Con’t) Diaphragm carburetors maintain a constant fuel supply by means of a flexible metal disk called a diaphragm. At rest the diaphragm is bent down forcing the fuel inlet valve closed preventing fuel from entering the engine.

32. Fuel System: Types Of Carburetors
Diaphragm Carburetor (Con’t) When the engine is started the diaphragm flexes pulling the fuel inlet valve open permitting fuel to flow into the engine.

33. Fuel System: Types Of Carburetors
Diaphragm Carburetor (Con’t) When the engine is started the diaphragm flexes pulling the fuel inlet valve open permitting fuel to flow into the engine. Engines equipped with a diaphragm carburetor can be operated in any position.