Fuel flow through carbs?

Trying to understand carbs before I open them up.

One thing that would help me is knowing how the fuel flows through the carbs

Here is a diagram of how I think fuel sits in the carb when not running (blue is the petrol)



But can someone add to it where the fuel flows and the air mixes with it on the diagram when the engine is running?

I would find that most helpfull in trying to understand the sequence of events.

Thanks

 

Have a look at these links,

Shows how the carb circuits work:
Carbs 101 PDF

Shows the bits and a simple diagram of the fuel flow:
Helpful Hints PDF

Hope they help. You should be able to see from them how the bits in your carb diagram relate.

Don't think the fuel level is as high as you show it.

Post number 300

 

The FUEL rises to a level about equal to the placement of the lock washers on the four screws securing the Float Bowl to the Carb Body.

The fuel passes through both the Pilot Jet and the Main Jet seeking the level allowed by the float height adjustment.

The Fuel that flows through the Pilot Jet is drawn-up through drilled-out passages, by the flow of AIR moving to respond to Engine Vacuum created by the engine's piston movement -- down -- with the Intake Valves OPEN, during the Intake Stroke.

The Pilot Air Flow is regulated by the Pilot Mixture Screw.
A The Pilot Mixture Screw is adjusted Out ... a greater flow of air is allow to enter the engine.

The Air drawn through the Pilot Air Passage, rushes over a junction where the air passage is open to the Pilot Jet's Fuel Passage.
The decrease in pressure above the fuel, there, causes the fuel to be siphoned-up, atomized and mixed with the the Pilot Air and is introduced to the Intake Vacuum through the Pilot Mixture port, just inside the Throttle Butterfly opening.

When the Throttle Butterfly Valve is Opened, the rush of air moving to satisify the Vacuum causes the sealed Diaphragm Assembly to rise, as the air within the piston is drawn away to satisfy the vacuum; too.

The reduced volume of air within the Diaphragm causes the Diaphragm Assemble to rise. As it does, the attached Needle valve rises and permits the air surrounding the Main Jet's Emulsion Tube to be drawn to the flow through the open throttles.

The Main Air surrounding the Emulsion Tubes through the drilled Main Air passages ... acts do draw-up Fuel in proportion to the amount of air allowed to escape up the Main Fuel passage as more metering ports and the main Fuel Passage is opened by the Needle valve as it rises under the effect of the reduced air pressure beneath it rushing into the cylinders.

The gas comes from a special place, on Earth, where the people there sell it for as much as they can possible get per drop.

 

Your fuel level is incorrect and actually defies physics. Draw a line from the bottom of the tip of the float valve across the float bowl horizonitally. This is where the fuel level will be. At the idle jet the fuel will drop down to this level ( and actually should show fuel in the middle section above the jet) and at the main jet the level will rise up past the main jet. The emulsion tube is made with a larger diameter collar at each end. This is where the fuel sits in a pool to be drawn from. This would be those narrow spaces beside the emulsion tubes. Remember that liquids will equalize and find the same level. So you physically can't have the level higher at the idle jet as your diagram shows.
The air from the air passages connected to the jets will regulate how much fuel can be drawn up by the main venturi action of the carb throat. The air jets being controlled vents to maintain and regulate the lower pressure Rick mentioned to suck the fuel up into the carb throat.
The idle jet has a very small pool to allow the tip of the jet to meter the fuel. The emulsion tube has the jet needle to meter fuel. Once at WOT and high engine speed the main jet is metering and the jet needle is not used having been pulled out of the way by the rising of the diaphraghm and piston.
The air as it travels faster will pull more fuel but these are constant velocity carbs so the air doesn't flow faster. The rising of the carb piston enlarges the venturi diameter and increases the mass air flow.

 

Thanks guys

I think I will need to print out all this info (I find it easier to study from paper than the screen) Combining the simplified explination in the web pages from Kiwi, and the more detailed info from both Rick and Blue I am confident I will master this. I will let you know how I get on.

Cheers