what is venturi. is it a bad thing on carbs

[sacramento_ford]

thanks for advice

[cmoore]

Venturi is a type of pump. It's normally associated with oil or water pumps, as it uses a rotating, finned hub to distribute the water at a high rate. I wish I knew more about carbs to answer that for you, but someone on here will have it for you soon I'm certain...

[fitzwell]

Venturi..as in one, two or four.. barrels on a carb.
see here..

http://en.wikipedia.org/wiki/Venturi_effect

and here

http://en.wikipedia.org/wiki/Bernoulli%27s_principle

[suavematt]

it's part of the carb' that gets JACK'd everytime the engine back-fires
Later!

~ Suave'

[suavematt]

it's part of the carb' that gets JACK'd everytime the engine back-fires
Later!

~ Suave'

[Happy_Camper]

Lets see if I can do this in three simple steps (haven't taught this for about 6 years):

Venturi is very good!
1). When you look down the big bore of the carburetor, there is a round ring shaped cylinder in the middle. This is the venturi. Because of the throttle plate in the bottom, there is not a high volume of air movement in the bore unless the carb is at WOT. So the venturi is installed as a restrictor. This causes the air speed to increase through and around the venturi. The faster the air speed, the lower the pressure for a given volume. All the fuel except the accelerator pump enters the bore through the venturi.

2). Vacuum is pressure. It's just negative pressure. High pressure pushes to low pressure. Just like the weather people talk about.

3). The ambient air pressure acting on the fuel in the float bowl is way high in comparison to the negative pressure in the venturi, so fuel is pushed by ambient air pressure, through the jets, and mixer (tubes with air bleeds, for improved cruise economy), and is pushed out the holes in the venturi.
The result of this should look like a fog, with little to no droplets.
As the throttle plate opens further, more air is pushed through the venturi. Vacuum (or negative pressure) rises, and more fuel is pushed out of the float bowl and through the venturi. The fog of atomized fuel gets thicker to mix with the increased volume of air.

So that's pretty much how it works. Without a venturi, fuel atomization is critically hampered. Driveability reliability, and economy are vastly improved by the use of Venturi. If you're interested, read up on "Annular Nozzels" which are the "next evolution" of venturi.

Clear as mud?

[lee_ford]

Lets see if I can do this in three simple steps (haven't taught this for about 6 years):

How about a little help from a student teacher?

1). When you look down the big bore of the carburetor, there is a round ring shaped cylinder in the middle. This is the venturi.

True, the part is called a Venturi and it has a venturi shape. Also to add, the barrel is itself a venturi shape.

Clear as mud?

How about this:
As air flows from the tight area inside the narrowest part of a venturi to the wider area below a venturi, the molecules of air have more space to fill and will expand becoming less densely packed. Less dense air is lower pressure air. This same effect explains the lift caused by the wings on an airplane. A Venturi is shaped like a wing bent into a circle.

As to the barrels venture shape: As this flow of newly mixed fuel and air passes into the wider area below the barrel's venturi, the molecules of fuel are pulled apart and a more combustible mixture is created. The barrel's venturi also helps pull more air through the Venturi helping it flow more air and mix in more fuel than without the barel's venturi.
I made a quick graphic. I hope it helps. (I should thank Disney for the science shows back in the 50s and 60s.)


Also, here is a link to another graphic from an Aquaculture Dictionary
http://www.aquatext.com/images/diagrams/venturi.htm

Please note: The idle fuel is sucked into the air steam below the almost closed butterflys. If you have ever looked down into a carb at idle, you do not see any fuel being mixed in. However when you open the throttle the fuel entering the air flow inside the Venturi opening becomes very apparent. Looks kind of cool too! Everyone needs to take a look at least once. Be sure the motor is tuned good and is not prone to back fires.