1: Orifices above float level or between the well and the nozzle allow bled air to raise the pressure (reduce the vacuum) in the nozzle and above the fuel in the well. That delays the initial start of fuel flow from the nozzle to a higher air flow through the venturi and is used to control the point in the early throttle opening where the main starts.
Less holes at top of E-tube will keep higher pressure difference between bowl and fuel well? This should advance (relatively) the start of fuel flow?
And help the gasoline keep up with the sudden high velocity of the air when mashing the pedal?
Possibly related to the documented issue with this carb, but I'm sure people have tried modding the E-tube before.
The fuel well is the the cylinder that the the E-tube/Main Jet screw into, correct?
2: Orifices at float level increase low range (early throttle opening) fuel flow by carrying fuel with the airflow to the nozzle.
More Holes at float level to help with more fuel delivery at early throttle opening.
So less holes at top, more holes in middle.... Just trying get an idea of how this info would apply to an optimized E-Tube design. Just some ideas of where I might look to mod an E-Tube for experimenting.
3: Orifices below float level increase fuel flow by the effect of lowering the level of fuel in the well to the hole(s) admitting air. This is like raising the float level a similar amount (increases the effect of gravity in the pressure difference across the main jet) and also adds to the airflow carrying fuel to the nozzle. Locating the orifices at different vertical positions influences this effect’s progression.
Still trying to wrap my head around this one.
4: The "emulsion holes" influence is greatest at low flows and the "main air bleed" has most influence at high flows.
OK now I got to learn the Main Air Bleed on my carb! lol
In the first three cases above, once fuel flow is established it is greater than it would be with fewer or smaller holes. Visualize wind blowing spray off of the top of water waves. It doesn’t take much pressure difference to cause the velocity of the airflow through the bleed orifices to have significant velocity in the orifice, even approaching sonic (1100 F.P.S.) if the orifices are small. The phenomena of critical flow is what limits the total air flow through an orifice and allows tuning by changing bleed size.
Less holes above float level, equal number of holes added at float level to help it off the line and keep total air flow (and hence fuel flow) similar at WOT once fuel flow is established?
Wonder if the 140 E-Tube fit in the 390?
I'll post pics when I get to it.
I'll check if HF has a hole re-locator, but this might require some solder if I decide to experiment.
