CarburetionFuel Delivery

Purpose: produce mixture of fuel & air to operate an engine

Basics:1. Air enters top of carburetor2. Mixes with liquid fuel3. Goes through passages4. Sprayed into intake manifold5. Burned in combustion chamber

Operates based on different pressures

Cylinder has no atmospheric pressureAir/fuel mixture is pushed into cylinder by

atmospheric pressure in the carb

Venturi principle- Restriction in a passage creates a vacume.

( Causes air to move more rapidly)

Carbs come in many styles & typesNatural draft- air flows horizontally into

manifoldUpdraft- a/f mixtures forced upward

toward engineDowndraft- gravity assists air into

manifold

Float type carburetorsFloat= maintains constant level of fuel in

float bowl

When fuel is used float unseats needle valve and allows fuel to enter the bowl

Choke- Round disk mounted on shaft at the intake end of the carb.

Closed= provides more fuel to the engine to allow starting

Adjusting needle- adjusts the amount of fuel entering the nozzle to be discharged.

Sometimes these are pre-set & non adjustable

Primer- hand operated plungerForces additional fuel through main

nozzle. Mainly used to start cold engines

Governor◦Maintain a selected speed◦Prevent over-speeding that could cause engine

damage◦Limit high & slow speeds

Air CleanersEngines must have clean air!Dust/moisture ruin engines

Servicing an Air CleanerChange ever 25 hours on lawnmowersFollow manufacturers instructions