and the float valve inside the bowl controls how much fuel enters the bowl. Then the fuel enters a jet and that jet sprays the fuel into a venturi which bottlenecks to add pressure which mixes the air and fuel together. Above the jet is the air intake, where the choke is. When the choke is closed it cuts off most of the air flow which increases suction, making the fuel mixter rich. (more gas than air)
Next air/fuel mixture hits the throttle plate, which when opened, the plate is vertical, letting in the most air/fuel mix it can, and almost closed because if fully closed the engine wouldn't idle. After that the muxture goes down the carb throat and into the combustionchamber.
Indentifly the components in a carb?
What are the holes in the emulsion tube for and how does it work? It mixes air from the air corrector jet with fuel from the main jet, and controls the mixture from the discharge nozzle at all engine speeds.
How does the manual choke and automatic choke work? The manual choke is opperated from inside the car, and is controlled by a flexible steel cable that moves the choke butterfly so you can start your car.
The automatic choke works by a thermostatic coil spring wheere tha butterfly shaft is and which exerts pressure to hold the choke valve closed, than the heat is applied o the coil after the engine is started it causes the coil to expand allowing the choke to open
What is the purpose of the float in the carb? The float in a carb controls the "float needle valve" wich monotors the amount ov fuel allowed to pass into the ventura, it is a simple design of a male/female type of valve as the fuel level in the float chamber rises and falls it opens and closes the needle valve.
What is the purpose and how does mechanical lift pump work? These pumps are usually bolted onto the engine block or head, because the engine's camshaft has an extra lobe that pushes a lever on the pump which is on a spring so the diaphragm moves both ways on one lever. On the down stroke to BDC the pump sucks in doing so the fuel inside the pump chamber increased, causing fuel to be drawn into the pump from the tank. The return motion of the diaphragm to TDC is accomplished by a diaphragm spring in the pump itself, during which the fuel in the pump chamber is squeezed through the outlet port and into the carburetor. The pressure at which the fuel is expelled from the pump is limited and regulated by the force applied by the diaphragm spring.
How does a vacuum fuel pump work on a two stroke engine? The carb doesnt have enough grunt to suck fuel all the way from the tank to the engine bt itself so there is a vacuum pump before tha carb in the "circuit" this pump works by a diaphragm which moves/works according to the piston stroke and atpospheric pressure, there are two 1way valves in the pump which ensures that the fuel lines don't get air pockets and the pump doesn't have to work as hard to deliver fuel.
What pressures would you get from these types of pump? around 2 - 5 psi
What the difference between petrol and diesel? diesel is c.i which we now know is compression to heat the fuelup enough that it ignites and forces the piston down.
Petrol is s.i and which is spark ignition, the vapour from the petrol is fighly flamable so a little spark would cause ignition easily.
How does the fuel shut off solenoid work? An electric current is pushed through a copper coil causing a magnetic field and therefor controlling the fuel supply when the car is off.
What is the four stroke cycle? Intake : exaust closed, intake valve open - B.D.C
Compression : exhaust and intake closed - piston on the way back up
Power : sparks at T.D.C
Exhaust : is pushed back to B.D.C then trvells back up pushing the fumes through the exhaust outlet.
What does S.I mean? Spark ignition
What does C.I mean? Compression ignition
When dismantling a carb what precaution should you take? do not turn it upside down because the small springs and valves will change position/alinement.
How does a bimetallic spring work in a automatic choke work? A bimetallic spring that helps with cold starting.when the engine is cold the sping holds the butterfly valve closed, as the engin heats up it slowly opens the valve producing a progressivly leaner fuel mixture. At the same time the high idle gradulay drops back to normal, when the engin is warm the butterfly valve will be fully open, ( standing up) producing the right mixture of air and fuel for the warm engine.
What is the purpose of the venturi and how does it work? it works on the same principles as a aeroplane wing - so it bottlenecks to make the air flow faster and the fule an air to mix more effectively
Explain how a fuel cut off solenoid is checked and why is it fitted? There are 2 wires on the back of the solenoid, you can pull them out and touch them together and listen for a click,if it doesn't it is not working, they are fitted to stop a fire if you crash etc
An engine lacks power. What is likely to cause this problem? it could be a number of things from the float, jets, fuel pump, injectors and manifold and exhaust leaks.
How do you adjust the float in a carburetor? look up the correct spacing it needs and use your feeler guage to set the gap accuratly
What is the purpose of a power valve? The purpose of the power valve is to turn on at a pre set vacuum level so it en-richens the fuel mixture with more fuel before the main jets are fully at work.
What are some of the causes of high fuel consumption? It could be because the carb is flooding, float level is to high, throttle is not set correctly, idle skrew not set properly or cracked fuel lines, to name a few
How is the the idle and mixture screw adjusted? Idle skrew, skrew it all the way in, then 1.5 turns backed off. Mixture skrew all the way in then 2 turns backed off.
When refitting a three mutiple carburettor what should be done after installing them?Check that all the butterflys open the right way with the levers, linkages and choke.
