Carburetor 1

Carburetor’s 1 

Indentifly the components in a carb?

The carburetor has many parts the helps the fuel come in and mix and supply fuel to the cylinder at a constant rate. This picture above shows that the fuel in brought in by the fuel line and filter which then goes into the float bowl then sucked up by a tube which delivers fuel into the throttle where the air is passing through which mixes the fuel and air into the combustion chamber. The throttle controls the air flow along side a venture. You can adjust the carburetor settings with the idle screws.

What is the purpose and how does  mechanical lift pump work?

The pump uses a spring which opens and closes a diaphragm which pumps the fuel from the inlet of the carburetor and the pushes it out the outlet. The spring has an arm which is connected to the camshaft and works on the cam lobe and as it lobe spins it pushes the spring up and down the faster the engine spins the faster the pump works and brings the fuel in and out.

What pressures would you get from these types of pump?

From these sort of pumps the pressures you would expect is about 4-5psi.

What is the four stroke cycle?

There are 4 strokes that a 4stroke engine needs to run which are:

Intake: Where the inlet valve opens bringing in the vaporized air/fuel mixture into the cylinder. The piston is moving down.

Compression: This is once the piston has hit bottom dead centre and starts moving upwards, the intake and exhaust valves are close which compresses the mixture until it is just about to the top.

Power: At about 8-10degrees before top dead centre the spark plug ignites the mixture causing an explosion inside the cylinder pushing down the piston causing the power to spin the crankshaft. The valves are closed until they hit the bottom.

Exhaust: Once the piston has hit bottom dead centre the exhaust valve opens as the piston moves up the cylinder it pushes the burnt gases out the exhaust. Then once it has hit top dead centre the exhaust valve closes and the intake opens to repeat the cycle.

What does S.I mean?

S.I is short for ‘spark ignition’ which only petrol engines use. This meaning that it uses spark to ignite the air/fuel mixture inside the combustion chamber unlike diesel engines

What does C.I mean?

C.I is short for ‘compression ignition’ which is the diesel engines way of igniting the air/fuel mixture inside the combustion chamber. It relies on the high compression and hot temperatures to ignite the mixture.

How does a bimetallic spring work in a automatic choke work?

This special spring is put inside the carburetor and is mounted opposite to a rod which turns the choke on and off. As the hot air is passed by it the heat bends the spring towards the contacts and once the engine was at operating temperature the spring will of bent into the contact which closed the choke.

What is the purpose of the float in the carburetor?

The float chamber (bowl) is the supply of fuel into the carburetor jet. As the fuel is used up there is a float inside the chamber and as the float drops it opens a needle valve which lets in more fuel into the chamber. But when the float chamber is filled the float rises and closes the needle valve which stops the fuel being let into the carburetor.

What are the holes in the emulsion tube for and how does it work?

The emulsion tube brings in the fuel from the float bowl and supply it up into the throttle chamber and as the throttle opens and there is more vacuum which sucks more of the fuel out of the holes in the emulsion tube. This helps to mix and atomize the fuel and air so the engine runs smooth.

What is the difference between petrol and diesel?

Petrol is lighter and has a lower boiling temperature then diesel, it also has a higher vapor pressure then diesel. But needs a spark to ignite under pressure.

Diesel is much heavier then petrol and also has a higher compression ratio compared to petrol. And has a higher boiling temperature and is a lot more dense then petrol and is ignited by the high compression in the combustion chamber.