4-Stroke EFI Basics for Snowmobiles: Part 1

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Carbs: Better or Worse?

By: Kent Lester

To understand the efficiencies of 4-stroke EFI you first need to understand the inefficiencies of carburetors.

Think of an aerosol spray can. Whether you’re spraying paint or hair spray, press the nozzle down and you’ll get a consistent, unending (until the can is empty) spritz of liquid.Carburetors work something like that.

When the engine is running, because of the vacuum or sucking effect of air flowing into the carburetor, gasoline is being sprayed as long as your thumb is holding the throttle open.

Every stroke or revolution of the engine whether intake, compression, firing or exhaust, the carburetor is delivering fuel. Although the cylinder’s intake valves regulate whether or not the gas is actually getting into the combustion chamber there’s always a range between the ideal amount of fuel and too much fuel being available.

The presence of too much fuel not only causes those annoying burbles and hesitations when you tip-in the throttle but can cause an idling engine to stall or can make start-up difficult and flooding too easy.

Air flow is another issue. Oxygen is your engine’s second fuel and if the balance between air and gasoline is off, the engine can find itself in a “too rich” environment where performance is affected or a “too lean” situation where excess heat is generated and the engine’s physical health is in jeopardy.

To get a cold engine started, carburetors depend on a “choke” or an “enrichener” to adjust the balance between fuel and air flow. Gradually, more air is introduced as the engine warms up.

Various manual, mechanical and electric choke devices have been added to carbs over the years with varying results. Certainly, with snowmobiles, the manually operated choke is most common.

Keep checking back for more on this 4-part series about the basics if Snowmobile EFI technology.

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