Carburetion Fuel Delivery

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

Basics: 1. Air enters top of carburetor 2. Mixes with liquid fuel 3. Goes through passages 4. Sprayed into intake manifold 5. Burned in combustion chamber

Operates based on different pressures Cylinder has no atmospheric pressure Air/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 & types Natural draft- air flows horizontally into manifold Updraft- a/f mixtures forced upward toward engine Downdraft- gravity assists air into manifold

Float type carburetors Float= 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 plunger Forces 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 Cleaners Engines must have clean air! Dust/moisture ruin engines

Servicing an Air Cleaner Change ever 25 hours on lawnmowers Follow manufacturers instructions