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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
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Carburetion Fuel Delivery
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