AirCooled Engine Technology...Ch 8 Carburetion Pages 129152. Air Cooled Engine Technology 1. The purpose of a carburetor is to produce an atomized mixture of & ___ which will

AirCooled Engine Technology

Roth 9 th Ch 8 Carburetion Pages 129152

AirCooled Engine Technology 1. The purpose of a carburetor is to produce an atomized mixture of __ & _____

which will efficiently operate the engine under all running conditions. Vaporized below the throttle plate.

Blood & Water Air & Fuel Pressure & Volume

AirCooled Engine Technology 2. Engines will not ignite liquid gasoline, so the carburetor must __________

the fuel to make it burnable. In addition, the carburetor must mix the air & fuel in the proper proportions.

Vaporize Atomize Categorize


Liquid Fuel

Emulsion

Engine Heat helps to Vaporize the A/F Mixture

The area below the throttle plate is also called the “Engine Side” of the throttle

AirCooled Engine Technology 3. More ________ is needed for combustion than fuel. 9000 cubic feet of air

is needed to mixed with every cubic foot of gasoline. This ratio is expressed by volume.

30’ 30’

10’

30 x 30 x 10 = 9000

1 Gallon Can of Gas

1 Gallon Jug of Milk

1 gallon ≈ 1 cubic foot

AirCooled Engine Technology 4. An average air/fuel ratio expressed by _______________ would be 15:1.

(14.7:1 is perfect for CAT operation) RICH mixtures have less air (8:1) LEAN mixtures have more air (18:1).

Distance Weight Volume

This ratio is expressed by weight.

Smaller #’s & easier to communicate than the volume ratio

AirCooled Engine Technology This ratio is expressed by weight.

Smaller #’s & easier to communicate than the volume ratio

AirCooled Engine Technology 5. __________ are air & fuel mixing devices operated by pressure differences.

Fuel Injectors Carburetors Catalytic Converters

AirCooled Engine Technology 6. In the study of engines, any pressure less than atmospheric pressure is

called ______________. There is no absolute vacuum in an engine since air is needed to make the fuel burn. (Bernoulli principle)

Vacuum Force Mercury

AirCooled Engine Technology 7. The pressure produced by the weight of air molecules above the earth is

called ________________ pressure. There is less pressure at higher altitudes and more pressure near sea level.

Atmospheric Stratospheric Tropospheric

AirCooled Engine Technology 8. Air always flows or is pushed from a ______ pressure to a _______ pressure.

Low to High Left to Right High to Low

Why does this work?

AirCooled Engine Technology Is blood pressure higher or lower than atmospheric pressure?

What are the implications?


AirCooled Engine Technology 9. A ___________________ is a restriction in a passage.

In a restriction air speeds ____ and pressure _________.

Bernoulli Venturi Lamborgini Up & Drops



“lift distance” in a carburetor is the dimension from the fuel level to the venturi Lift

Fuel Level

Lift Distance

AirCooled Engine Technology 10. ____________________ is the action of breaking fuel into small particles

and mixing it with air. The atomized air/fuel mixture is sometimes known as an “emulsion”. Emulsion occurs in the venturi.

Atomization Vaporization Condensation

AirCooled Engine Technology 11. Classified by direction of air flow, carburetors may be ____ draft, _________draft, or _________draft.

Updraft Downdraft

Side draft or

Natural Draft




F.

B.

A.

C.

E.

D.

AirCooled Engine Technology 12. A basic carburetor uses 6 systems or circuits to provide the correct air/fuel

mix for all conditions.

AirCooled Engine Technology FCLAMP

SYSTEM PURPOSE OR FUNCTION

Keeps a constant supply of fuel near the venturi for quick use in other systems Provides a rich air/fuel mixture needed for starting and cold operation Provides just enough fuel for economical, low speed operation Adds fuel to the emulsion for the transition from low speed to medium or high speed Provides the correct emulsion for partthrottle (medium speed) power demands Used for Wide Open Throttle (WOT), high speed operation

Float Choke

Low Speed Acceleration Main Metering

Power Enrichment

AirCooled Engine Technology 13. When the fuel level rises in the float bowl, the float also rises and pushes

the ________ valve tightly into the seat to stop fuel from flowing in. As the fuel level drops, the float pulls the needle out of the seat, allowing more fuel to enter the bowl. Needle & Seat are serviced as a matched pair.

Needle Pin Bolt

AirCooled Engine Technology 14. Label the lettered parts of the down draft, float carburetor.

A.

B.

C.

D.

E. F.

A) Choke Butterfly B) Venturi C) Throttle Butterfly D) Main Discharge Nozzle E) Needle & Seat F) Float

AirCooled Engine Technology 15. A ________________ is a handoperated bulb or plunger which, when

depressed, forces additional fuel through the main nozzle for cold starting. They are used in place of choke systems on some carbs.

Primer Shiner Enricher


AirCooled Engine Technology 16. A ________________________ carburetor does not have a float, but has a

flexible disc (diaphragm) operated by pressure & vacuum impulses which works to keep fuel near the venturi for quick use.

Primer Diaphragm Enricher

AirCooled Engine Technology 17. A ____________ takes away the need for the operator to constantly adjust

throttle position regardless of changes taking place in engine loads and power demands.

Principal Governor Manager

chainsaws & string trimmers do not have governors

engine speed is controlled by the operator finger

on the throttle

AirCooled Engine Technology 28. A governor will MAINTAIN the speed selected by the operator,

prevent OVERSPEEDING, which could damage the engine, and will LIMIT both high and low speeds of the engine.

AirCooled Engine Technology 19. Governor types include: 1) ____ ____ (pneumatic), _________ (centrifugal),

vacuum operated, & electronic governors that use a limited angle torque motor on the throttle shaft.

Weather Vane & Mechanical Air Vein & Electric Air Vane & Mechanical

AirCooled Engine Technology 20. The governor _____ always tries to pull the throttle to a wide open position.

(WOT)

AirCooled Engine Technology 21. The air vane or the flyweights always try to pull the throttle to a fully

____________ position.

AirCooled Engine Technology 22. The speed where the spring & air vane/flyweight forces balance out is

called _______________ speed.

AirCooled Engine Technology 23. In the case of lawn mowers, blade tip speed must not exceed _________

feet per minute (215 mph). It is recommended to set maximum engine speed to 200 RPM less than maximum blade tip speed.

19,000 1,000 1,000,000

19,000 x 60 = 1,140,000 ft/hr 1,140,00 ÷ 5280 = 215 mph

AirCooled Engine Technology 24. The longer a lawn mower blade, the ________ the maximum RPM must be.

Faster Slower Denser

AirCooled Engine Technology 25. Erratic or oscillating engine speed is known as governor ______ or surging.

Hunting Droop Kicking

Governor: A governor is a device that automatically opens the engine's throttle when more power is needed and closes it when the load is light.

AirCooled Engine Technology 26. Hunting, surging, and governor droop can be caused by improper ________

adjustment, (usually too lean), governor parts or throttle shaft binding, and by damaged governor springs & links.

Carburetor Timing Height

AirCooled Engine Technology 27. ________________ & _______________ are 2 very important governor

operating characteristics.

Stability & Sensitivity Starting & Charging Spark & Compression

RPM hunting & surging on a lawn mower is less critical than in a power generation situation…

AirCooled Engine Technology 28. Air filter variations include: _______wetted foam, _______types which

can be treated paper (disposable), felt, fiber, and flocked screens (washable & reusable) and ________element. (best of both)

Oil, Dry, Dual Water, Dry, Dual Oil, Element, Duel








Reverse Venturi Effect








Closed Throttle Idle Part Throttle Idle








G

F

E

D

A

B

C

H



What’s the Purpose?







E

H

A

B C

G

F

D
















Documents

AirCooled Engine Technology...Ch 8 Carburetion Pages 129152. Air Cooled Engine Technology 1. The purpose of a carburetor is to produce an atomized mixture of __ & _____ which will

AirCooled Engine Technology...Ch 8 Carburetion Pages 129152. Air Cooled Engine Technology 1. The purpose of a carburetor is to produce an atomized mixture of & ___ which will