STARTERS AND ALTERNATORS

Inertia starter
An inertia starter motor works by throwing the pinion into mesh with the fly wheel at high speeds causing the engine to turn over. this is achieved by electrical current flowing through the magnetic shoes causing the armature to spin which then throw the pinion into gear. Once the pinion has forced the fly wheel into rotation the side of drive would change, making the pinion clutch engage retracting the pinion.

Pre-engaged starter
This starter works and relys on the solinoid which uses a lever/linkage to enguage the pinion before it starts to spin, this system means that there is minimum wear on the teeth.

Alernator
An alternator is an electromagnetic unit that is driven by a belt from the motor this means it wont run under its oun power. This is a rotor that cuts the magnet feild made by the coil and shoes, it turns within a stationary set of conductors called a stator. As the rotor is driven it cuts through the magnetic field causing the current to change producing an alternating current. This current changes due to the different polarity of each side of the magnet. This current is then feed through a rectifier which stabilises the voltage to a direct(DC) current. The alternator is used to power the electrical systems of the engine once started and charge the battery so it produces around 14 + V

BUISNESS PRACTICE

Warranties
When you buy a product e.g. an outboard it may come with a description of what it will do for how long but in the fine print it might say you have to run the engine on non synthetic oil and stay under 5000 revs and to flush it out for 7 minutes minimum. it is important to read all of the small print because a warrant is a legal document that assures you that it is going to work properly.

Guaranties
a guarantee is what the name is - if you buy a new part or have a new part installed professionally, the workmanship and life of the part being installed is usually guaranteed, so if the new part were to fail you wouldn't be expected to pay unless you did something against what the legal warranty said.

Quotations and estimates
A quotation is an agreement between both parties of what the job will cost this can be a range from x to y  but if the final price exceeds this you may be facing legal charges.
An estimate is a rough guess of how much you think the job will cost, this is not a legal bond like a quote so it is important that you make yourself clear to the customer what you are giving them so there is no grey areas.

Charge out rates
when deciding on a charge out rate it is important to take into account your overheads, employers and yourself. All those into consideration a $60 per hour charge out rate is not so steep.

Courtesy arrangements
these can be anything from cleaning the inside and outside of the car, checking tyre pressures, cleaning the inside if headlights, giving the customer a ride home (if local) and even offering a temporary car whilst theirs is getting fixed. All are done to keep the business turning over and money coming in.

Cultural issues
Because the world today is not split into races and cultures it is important to accomodate for difficulties, these  refer to expectations, Practises, Communication issues e.g. being clear on the phone etc.

MARINE TRANSMISSIONS

Outboard gear box
This system runs from a pinion wheel directly from the engine which turns 2 gears at the same time, however only one is ever engaged and driving (under power) by way of a dog clutch.
The gears are selected by a selector rod which has a slot on a slant that moves the dog (that is fixed to the prop shaft) into the desired forward or reverse gear.
the gears are helical tapered gears which run directly onto the prop shaft.

Stern leg system
Unlike the outboard gearbox the stern leg transmission is vertically positioned on the shaft that drives the prop shaft. The clutch system unlike the outboard dog with teeth the stern leg clutch is a tapered system that will engage either forward or reverse depending on the position of the selector shaft.
At the end of the drive shaft where the prop shaft joins is a pinion wheel and one or two permanently engaged gears - if the engine is duo prop or single props.

Inboard gearbox
An inboard gearbox uses hydraulic fluid to compress a clutch pack which therefor engages the prop to move forwards or backwards. The concept of this system is much like a motorbikes.

What type of gears are used in stern legs and outboards?
tapered helical cut gears are used in outboards and stern legs because the offer the best contact between teeth all the time especially on the pinion - this type of gear also reduces noise.

The duo prop system
This works by having a pinion drive and two constant mesh gears rotating in opposite directions and moving one shaft inside the other. a propeller is fixed to each of the shafts which are rotating in different directions, this means that one of the propels has to be cut counter rotational drive so the engines props are always moving the boat the same way whilst the props are not.

The "V" drive system.
this gear box is to change the direction of the drive shaft, it also enables you to focus the majority of the engines weight further back in the boat. it does this through 2 stages in the gear box
1. the drive shaft enters the gear box and drives the first stage which is 2 shafts the first one is the one that the drive shaft is turning, it has straight cut teeth that drive a chain that turns the next shaft which also as well as having the straight cut teeth and chain linkage, has a tapered helical cut gear on the end of it so it acts like a pinion.
2. the second shaft drives the output or third shaft on the helical cut tapered gear - allowing for the change in direction.

Jet unit and Surface drive.
A jet unit has a water intake on the bottom of the boat, the water is then pushed through a prop in the tube causing the water to exit under very high pressure (enough to push a boat). this type of drive is very effective if you are going over shallow sand bars or shallow rivers etc.
A jet unit is especially good at turning this is achieved by moving a cap over the water out put and directing it  to where ever you want without loosing power, this is why a jet boat can turn almost 180 degrees without moving.
The downside to a jet boat is that you have to be under power to maneuver the boat otherwise you will just drift.
A surface drive works on the theory that the more you have in the water the more drag you have and the slower you will go. a surface drive always has one blade out of the water at any time, this is so you accelerate faster, there is less drag and you use less fuel.

Gear BOX ;D

What type of gears are used for a reverse manual gear box? Explain?
in the Toyota 3k/4k gear boxes we were stripping and rebuilding the reverse gears were straight cut instead of helical cut gears this is because the reverse gear runs off of a neutral third sprocket which fits in between the driven and driver to change the way the output shaft is rotating. if the gears we helical cut it would make it very difficult to mesh 3 gears, whereas straight cut teeth slide straight in.

What type of gears are used for all the forward gears in a manual gear box? Explain?
the type of gears used in a manual gearbox to go forward are all helical style gears this is because more than one tooth is engaged at one time making it quieter than straight cut gears and stronger because of the amount of gear that is meshing with one another, this however causes thrust because of the angle of the teeth meaning thrust bearings are required. On heavy duty equipment like bulldozers etc a herringbone cut gear is used this is because more than one gear is engaged at one time and there is no thrust pressure on the shaft.

What is the purpose of a syncromesh unit? Explain
The purpose of a syncro mesh unit is to make the gear changes smooth. The name gives its job away -
it makes sure that the theeth on the two gears about to be enguaged or meshed together are spinning at roughly the sames speed so that your gears dont clunk as they mesh at different speeds. The way that the two gears are slowed to rotate at the same speed is with the brass baulk ring (a brass ring with a row of teeth and a tapered face). it is brass so that the soft metal will wear out faster than the hard shaft, it is also cheeper to replace. it is tapered because two tapers grip extremely thourghly but can also split easily.

How do you check a baulk ring for serviceability?
to check a baulk ring you need to see how close the ring is to the gear if it is able to touch the gear, the taper on the baulk ring has worn down too much, there needs to be a gap. (measured with a feeler guage) The gap would suggest that the tapers are tight against eachother and would do their job.

what is the pupose of a baulk ring?
the purpose of a baulk ring is to mach the speed of the two gears about to be engaged, it does this by having a tapered face which maches the taper on the gear causing the two to spin at the same speed when the two tapered faces are pressed. this system is important because it means that the gears when selected and changed are not under as much load because the speeds of the two rings are spining at almost the same speed.


What type of bearings are used in a gear box?
tapered roller bearings and thrust bearings, both of these bearings are to minimise any side to side/end to end movement.

Give an explanation of a gear ratio.
the way that gear ratios work is from low ratio (torque) to high ratio (power), the input shaft, 1st gear is the smallest gear, 4th gear is usually 1:1 or close meaning the same size gear on the input and output shafts whereas 5th gear on the input shaft is bigger than the corresponding output gear (also known as an overdrive gear).

ENGINE REFLECTION

Toyota 4 A-FE. 1600

To start we split the head from the block because we were working in pairs.
Cylinder head
once everything is dismantled and in order it is imortant to measure each component (if it is not visibly damaged) this is because the parts inside an engine have all got clearences.
cylinder head itself
we visually inspect the head to make sure that is not scored, pitted, chipped or worn. We check for these signs of damage because pitting and scoreing could cause a build up of carbon causing excess heat, if it is worn through to the water jacket a loss of compression can occur.
once the visual inspection is done run a straight edge over the surface to determine if the head is twisted or warped, if it is planeing can rectify the problem to an extent otherwise it is a throw away job.


valve stems to valve guides
the reason why we make sure that the clearences are within specifications is because oil will be able to travel freely to and from the head to the piston bore, it also means that the valve could sit unevenly on the seat if the stem guids are worn to much. We also check the stems for bending and wear visually and with vernier guages, we also check the springs and collets to see if they are in good opperating condition otherwise the valves may not be pulled onto the seat hard enough or fast enough.


Cam shaft
Like the other components the shafts are visually inspected for wear, bending and corrosion but because it is hard to visually check the lobes for wear so we use a micrometer and we messure from the base to the nose because if it is worn to much the valve timing will be out.
Another thing to measure on the camshaft is the journels these are checked with a DIT guage which determines if there is any ovality or twist in the camshaft - both of which would effect how even the spin of the shaft is.
The camshaft bearings have to checked with a plasti-gauge to determine whether or not the gap is suficient to allow for lubricating oil to travel through the slot to be transfered onto the shaft, this is because of the huge amount of friction/heat. An important thing to know when it comes to the oil grove is that it increases in width as it is torqued down.



 Camshaft valve buckets
The valve buckets in this particular engine run with a pad of a certain thickness on the top of the bucket, the thickness of the pad determines how far the valve spring is compressed and how far the valve itself is opened. It also means that if wearing occurs it wears the pad which is easily replaced and not the whole bucket.


Cylinder block
Cylinder bore
We visually check the bore for pitting and scoring then we measure it in 6 different places within the bore these measurements when woked out tell us how much ovality and taper is in the bore from the stress the piston puts on the block especially on the thrust side.


Piston
-Again visually inspect for wear, check the piston rings are all intact.
-Measure the piston on the trust sides just above the skirt to determine how much wear has occured and compare it to the secifications.
-Measure the gap between the ends of the piston rings to make sure that they are going to hold compression from entering the crank shaft housing.
-The conrods need to be checked on a special straight edge tool to see if they have been bent or twisted because if they are damaged they will put unnecessary stress and force on the conrod bearings and crankshaft.

 
Crankshaft
Once we have inspected the crankshaft for damage we check the journals for runout using the DTI guage, the crankshaft has to be very strong to accomodate for 4 pistons running on top of it so it has to be turning exactly true within the bearings.


Important to remember
Always torque the crankshaft bearings, conrod caps and head in sequence and to specifications.
  

OHC vs Push rod and Side valve

over the years there have been a few different ideas for an efficient and cheap engines from k cycle to rotary, but only 2 have prevaled to be produced in mass OHC and Push rod

K-CYCLE

ROTARY

OHC
over head cams can be single or double shafts per cylinder head, they can operate straight on top of the valve buckets with spacing pads or the play in the valves can be closed by a hydrolic system controlled by the oil pump.
OHC can also controll rockers which push directly on the valves.
DOHC ment more valves in a smaller combustion chamber which resulted in more power, the earlier models of DOHC ran on 2 seperate gears but now one of the gears is run off the other by a scissor drive, this means that money is saved on manufacturing because it is that much more narrow.

compared to push rod OHC
-is more expensive because of the seperate head.
-more efficient because ther is no air pressure lost down the pushrod guide itself.
-harder to time with belt and chains because some push rod engines are run of gears.
-in an OHC there are more working parts than on a pushrod engine e.g. long timing chains/belts, hydrolic tentioners and oil feeders to the cams themselves.

A side valve system is essentuly a pushrod engine minus rockers with the valves directly on the end of the rod. - more jurasic park style

blogger comment

i rekon blogger is wikid because you can do your work in your own time, it is on going and you can bounce ideas off other fullaz in the class

COOLING

Explain the terms ( Kinetic energy) Conduction,convection and radiation? Conduction is heat energy moving through a solid e.g. steel. Convection is the cycle ov heat through a liquid as the hot liquid rises the cold falls. Radiation is heat being transfered to the air from a hot object e.g. the engine

Indirect cooling? The coolant is in a closed cycle but still uses the raw water to cool the coolant further, this is a effective way of heat control because it works the same way as a car engine on a thermostat which means less corrosion and a faster warm up.

Direct cooling? The direct cooling method is to pump raw water up and through the water jacket then back out with the exhause fumes, this isnt as effective or practicle as indirect because of the corrosion and how long it takes for the engine to heat up - costing you more fuel.

What are the the problems you get with indect and direct cooling? Corrosion is the biggest problem because the raw water is so destructive, maintanance on the indirect cooling can be a mission - depending on how easy it is to get to the heat exchanger. You also have to regularly check the inlet valves because the can get blocked - causing over heating.

What is the puppose of a thermostat? To allow the engine to heat up to optimum running temp before letting the coolant pass through to be kept constant so the engine is always at the right temp.

Pressure cap? The pressure cap is a release valve for when/if the pressure in the radiator becomes to high for the specifications, it is also the way to top up the coolant.

Why is engines fitted with a core plug, and what is the purpose of a core plug? The manufacturors put them in so when they are moulded the can shake out all the core moulding sand. another reason for the core plugs is so if the water in the water jacket freezes it won't crack the block or head it will push out the frost plug instead.

What is the purpose of a heat exchanger? A heat exchanger is the equivelant to a radiator on a car except instead of cooling the coolant with air you cool it with raw water from the ocean which is also cycled to keep cold. It works by raw water circulating through pipes next to the circulating hot coolant the heat is transfered to the raw water leaving the coolant colder.

What is the core of the heat exchanger made of? Aluminium or copper because they are light weight and dont corrode very easily. 

How does the centrifugal circulating water pump work?

How does a raw water pump work?

Why is it important to lubicate the impellor when fitting from new?

When fitting a impellor what should you check before refitting the housing and why?

What is the purpose of a oil cooler and how does it work?

What is the process of a intercooler/aftercooler how does it work?

Why do we have Inhibitors & antifreeze?

How do you test Antifreeze?

What is cavitation corrosion?

What is galvanic corrosion?

Describle the terms

Stray corrosion?

Stress corrosion?

Corrosion Fatigue?

Crevice corrosion?

What is Electrolysis?

How do you prevent corrosion?

Why and what is bonding in the marine industry?

What are sacrifical anode made off?

Where would you place them in the marine industry?

10.06.11

What is the purpose of a water muffle?

2 - STROKES

Explain how a two stroke engine works?

















What is happening below and above the piston?
Explain what is meant, by scavenging when applied to 2 stroke SI engines?
Why must roller and ball race bearings be used on 2 stroke SI engine crankshafts?
Why are rollers caged in crankshaft bearings?
Why must ‘split’ type bearings be used on one piece crankshafts?
Why do we have pins between the piston ring gaps on a 2 stroke?
How does a reed valve work on a two stroke?
How do you check a reed valve?
Explain the term ovality and taper and how are they formed?
How does the piston rings seal in the bore?
What is meant by the terms groove depth, side clearance and end gap on the pistons rings?
Explain the difference between a 2 stroke and a 4 stroke engine?
What is meant by each of the following terms:
(a) Mechanical Efficiency(b) Thermal Efficiency(c) Volumetric Efficiency?
List 2 methods of lubricating the internal parts of 2 stroke S.I. engines?

28/06/11
What happens if the piston gap is too big?
What happens if the piston gap is too small?
How does a 2 stroke diesel engine work?
What is happening below and above the piston?

Explain what is meant, by scavenging when applied to 2 stroke SI engines?

Why must roller and ball race bearings be used on 2 stroke SI engine crankshafts?
Why are rollers caged in crankshaft bearings?
Why must ‘split’ type bearings be used on one piece crankshafts?
Why do we have pins between the piston ring gaps on a 2 stroke?
How does a reed valve work on a two stroke?
How do you check a reed valve?
Explain the term ovality and taper and how are they formed?
How does the piston rings seal in the bore?
What is meant by the terms groove depth, side clearance and end gap on the pistons rings?
Explain the difference between a 2 stroke and a 4 stroke engine?
What is meant by each of the following terms:
(a) Mechanical Efficiency(b) Thermal Efficiency(c) Volumetric Efficiency?

List 2 methods of lubricating the internal parts of 2 stroke S.I. engines? Premix - with the fuel 250ml oil to 1L petrol. Oil injection, a hose from the oil pump feeds to the space where the venturi meets the reed valve which is then delivered into the boar.

What happens if the piston gap is too big?
What happens if the piston gap is too small?
How does a 2 stroke diesel engine work?

DIESEL

Who invented the diesel engine and when? In 1893 by Rudolf Diesel


What fuel pressure would you get from a diesel pump? 15 psi - 18 psi in the new engines

How does the diesel pump work and why do we need to time the pump? The pump has to be timed so it delivers fuel at the right time and not for example when the piston is a BDC. The pump runs straight off the crank shaft so as the motor is running more slowly it pumps less fuel and when it is pushed to go faster the pump pumps more fuel to the engine.


How do you time the pump and with what equipment would you use? To time the pump you start by taking of the cam belt then lining up the notches in the sprockets with the marks on the block, once this is gone put the belt back on making sure the marks are still lined up. Now use the DTI gauge to set the motor to specifications. (sometimes you have to take off the pump to get the cam belt off).



What is the purpose of a glow plugs and how do you test the circuit? Glow plugs heat the air so it is hotter than the outside temperature, at this point it has also expanded because of the heat which would make the diesel ignite more effectively as a result of a more compression. You can test the each plug by measuring the resistance there is through each glow plug using a multimeter (if it reads approximately less than 5 ohms the plug is not defective). You can also test it straight from the battery (using jumper leads) if it works the plug will glow like a hot element.


Why do we need an lift pump on diesel engine? to supply/feed the diesel pump with fuel so there is no unnecessary stress on the diesel pump to pull and push fuel.


Why do we need a electronic fuel shut of valve? So that in a emergency there is a much lower chance of an explosion because there is no fuel traveling near exposed sparks etc

What is the knock sensor for and where is it situated? The knock sensor works by simply retarding the timing until the detonation stops. There is a significant decrease in power as it retards it also saves the engine from detonation which will break pistons and burn up head gaskets, The knock sensor is usually on high compression engines e.g. turbo's, performance cars and diesels an is located on the bloch of all cars.


How does the diesel injectors work? The fuel is delivered to the injector at a low pressure (5 -10 psi) by the diesel pump, once there it is pressurised to 2000 - 6000 psi, once the pressure is high enough it sprays into the compression chamber. http://www.youtube.com/watch?v=JgbuE1FT5Ks

Why do you need to bleed a diesel engine after replacing a fuel filter or removing the pump? Because air pockets might occur making it hard to start and could damage your starter motor.

How do you bleed the system? Pump the big primer button before you unscrew the metal fuel lines just a little bit so that the fuel can escape. Turn the engine over but don't start it until you see fuel spray from the base of the lines where the are screwed down.

How does a turbo work? A turbo runs straight from the exhaust which spins



Why do we need a turbo fitted to a diesel engine? Mainly to improve peformance because diesels are such torquie engines you wouldn't get much speed at high revs, more fuel and air adds alot more speed.


What is a supercharger? This is pretty much a air compressor because more fuel and more air = more power they are belt, chain or gear driven so power to the wheels from the throttle is instant.


Whats the difference between a turbo and supercharger? A super charger uses belt or chain driven pulleys to force more air and fuel into the combustion chamber, it also takes horsepower to make horsepower so there is no lag. A turbo charger takes pressure from the exhaust to spin a turbine which compresses and forces more air into the engine. Because a turbo runs off the exhaust is doesn't use any horsepower from the engine to make more, the only down side to a turbo is the lag as it winds up.

Why do we need a after- cooler or inter-cooler fitted to a diesel engine? The air coming from the exhaust is hot so it is ppushed through an intercooler which cools the temp, the turbo then force feeds the engine with more air. Because the air is cold is is more dense so even more oxygen is therefore in the bore getting compressed.


What the difference between in a direct-injection ( DI,) an indirect-injection ( IDI)? D.I has the injector spraying "directly" into the bore so it can be compressed by the piston at TDC resulting in ignition. I.D.I injects the fuel in a mixing/swirl chamber just above the bore with the glow plug which is then compressed.




What is the purpose of an governor? There are hydrolically, pneumatic and mechanical governors all of them do the same job which is to control the engines idol speed and top speed.


What is the difference between a diesel and a common rail diesel? A diesel engine is mechanically timed and has much less pressure in the fuel rail, a common rail diesel engine has very high pressure through the fuel rail and everything is electronically controlled and monitored making it more efficient and more powerful.

http://www.freeengineinfo.com/knock-sensor.htm
http://www.ehow.com/how_5183612_test-glow-plugs.html
www.wikipedia.com
Perrin Robinson
Ricardo Macedo

FUEL INJECTION

ECU- Electronic control unit? The ECU is like the brain of the engine it sends and receives messages of what the motor is doing, it controls and monitors the rest of the minor sensors, changing things like air flow and fuel mixtures to make the engine run to the ideal specifications.


Mass air flow sensor? It monitors how much air is entering the system then sends the message to the ECU so the amount of fuel to air mixture is right

Air Temp sensor? This is a very important sensor in the (car) because depending on the density/temp of the air the amount of fuel has to be changed because otherwise the fuel mix might be to lean or to rich - Hot, light air, less fuel needed. Cold, dense air, more fuel needed. If the motor is running wrong mixtures you might end up fouling the spark plug, consuming to much petrol or have a lack in power.

TPS throttle position sensor? This is located on the butterfly shaft and sends the ECU info about the position so it can monitor how much fuel to be injected etc

Throttle body? To control the amount of air taken into the engine.

Temp sensor? Tells us when the engine is cold and hot


fuel rail? The fuel rail is mounted next to the injectors and its purpose is to deliver equally pressurised fuel to the injectors.


Fuel pressure regulator? Is to maintain a constant fuel pressure above the intake manifold pressure.

Injectors? Injectors spray a mist of fuel into the cylinder


Idle air control? The idle air control is to change the engine idle RPM by opening and closing an air bypass channel inside the throttle body.

O2 sensor ( lambda sensor)? Measures the amount of oxygen is being used in the engine, which the determines if the engine runs lean or rich.

Map sensor? The map sensor reads the manifolds constant and instant pressure so it can determine the air density which is then sent to the ECU.


Plenum chamber? The plenum chamber is to equalise pressure entering the motor for more even distribution. A plenum chamber can also work as a silencer device.


Camshaft & Crankshaft sensor? These sensors tell the ECU where the shaft is in its rotation, this then determines when the fuel is delivered and when the spark is set.

Who invented fuel injection and when? The inventor of fuel injection was Herbert Akroyd Stuart in 1885.

Explain how an single and multi injection system works? Single - is a petrol injection point where the fuel and air is mixed by one centraly positioned injector. the injector is mounted on the throttle body and injects the fuel on top of the throttle to be sucked into the boar.

Multi - Uses one injector for each piston. the injectors are mounted on the intake manifold and inject the fuel into the top of the boar.

What does EFI stand for? Electric fuel injection

REFERENCES
http://ricardodemacedoengineer.blogspot.com/
www.wikipedia.com

CARBURETTORS

How does the carb work marine four and two stroke? The 2-stroke Carbureta works the same way as a 4-stroke carb does. There are fuel lines feeding into a float bowl, almost like a fuel resivoir
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.