Jul 15, 2010
If you’ve followed any of the builds we have done at Guilty, you realize one thing. We don’t like complicated! Zip. Nada. We just don’t like things that will strain the brain too much…plus there is only so much you can squeeze into a peanut shell besides rock-a-billy music, brands of beer to buy, our wives grocery list and how to work the remote for the tv. Thus, you’ll ONLY find “constant velocity carbs (or CV’s) on our bikes. Here is our simple explanation of how the “The Carburetor” works. (Que the cool theme music please!)
Some background info first: The carburetor is an integral part of the internal combustion engine. Internal combustion engines operate by igniting a mix of fuel and air. The fuel, (typically a combination of gasoline and air) is trapped in a combustion chamber in the engine. An engine is made up of several combustion chambers, also known as cylinders. The cylinders have moveable pistons at one end. When the cylinders are filled with fuel and air, the mix is ignited by the spark plugs. The resulting explosion pushes the piston out of the cylinder, which powers the engine. Remember the key word here: Suck, Bang and Blow. The job of “The Carburetor’s” is to ensure that the air and fuel are mixed properly and are in the correct amounts. Too much fuel vs air equals “flooding”. And too little fuel to air mixture will mean it’s too lean thus resulting in an engine not igniting and running rough. In a conventional carburetor, the action of the piston rebounding from the explosion returns the piston into the cylinder, drawing air through the carburetor. This causes the pressure in the carburetor to drop, drawing fuel into the carburetor to rest in a bowl containing a float. When the float reaches the top of the bowl, it closes the valve so that no more fuel can get in. As the fuel is used up, the float lowers, re-opening the valve to allow more fuel in.
In a constant velocity carburetor, (aka CV carburetor), the process is different. The CV has a device called a venturi, which is a tube through which the air enters the carburetor. The venturi is shaped like a funnel, narrowing at one end in order to change the air pressure of the air entering the carburetor. The narrow end lowers the pressure of the air, creating a comparative vacuum, which pulls fuel into the carburetor. The vacuum effect of the venturi is constant, providing a constant and consistent stream of fuel into the carburetor, as opposed to the pumping effect of a conventional carburetor. Thus it’s vacuum that works your bike’s carb. So, it’s the “Suck, Bank and Blow” scenario all over again!
glad we can lighten your day Chessie! Ride safe!
this was a fun read. a good way to learn anything…including about cv carbs.
thanks guys… I wish I could find someone who can figure out why I have 2 places in my rpm where the engine acts as if there is no more power to get…then all of a sudden I have a shotput effect. The 1st happens at 2k the second at 31k. So what do you think is going on? Oh wait…do you like challenges? I wonder…maybe the guys on PBR Click and Clack can help me? ;~) Good reading here guys, thanks.