Fuel level behind the bleeds

[kgb]

No, I have Dave Emanuel's book on Holley carbs, they label it Z08, but I see online there is a similarly titled book with the name Vizard. Shouldn't be too hard to find a copy, worth it if it addresses all questions on fuel levels in the air well during all stages of operation.

The MD 750 has downleg boosters, bought new. However, I stripped two bowl screws in it a few years into use and replaced it with another that a builder in Florida had on hand. I believe that was about the time Holley bought out BG, as that builder was getting out of them at the time and told me it was still new. So I'll take it as true it is as new as the original I bought.

Which aspects of a build do you need to know to determine fuel levels in the air well during operation? I'm sure some have greater bearing than others, just not which ones.

My primary assumption, this early in the process, is if you're cruising along at 3500rpm and running solely on the main circuit of the primaries, the fuel level in the well has dropped to at or below the level of the lowest e-bleed. Maybe not, depending on the size of the main bleed, or maybe more specifically depending upon the air flow characteristics through that jet compared to how it flows at each e-bleed, which would determine the amount of downward pressure (atmosphere) felt by the fuel and therefore its likelihood of joining the fuel flow in the main circuit or allowing some of the passing fuel to leak into the air well. That's what I've been looking to see addressed on these forums.

[rgalajda]

To start there is no air well in a typical holley 2 circuit metering block.
There is a Main Well in line with the main jet. Fuel from the bowl enters thru the main jet to the main well. The PVCR also enters to the main well.
The emulsion bleeds are drilled into the main well. Some early Holley carbs had an emulsion tube in the main well. This can be identified by a solid brass cap , as opposed to to a recessed cap for the main well. This is the inner of the two , viewing from the top of the metering block.

Next to the main well is the Idle Well.
Fuel travels from the bottom of the main well via a port to the idle fuel restrictor ( early Holley carbs ) and enters the idle well . From here it travels up the Idle well where fuel meets with air entering from the Idle Air Bleed.
Next it travels down the Idle Down Channel and exits the curb idle discharge and idle transfer .

Note: the IFR can be at the top of the idle well either under the brass cap ( some early holley’s ) or like newer carbs at the top of the idle down channel.

Main Well
Air enters via a channel connected to the High Speed Air Bleed ( air corrector ) which travels down the channel to the emulsion bleeds , where air can enter the main well fuel.
Maybe this channel is what your referring to as the air well ?

The metering block gasket seals this air channel.
Now if you add fuel to the main well it fills to the float level. The fuel travels thru the emulsion bleeds
to the air channel . So in a static level the fuel in the air channel will be the same as the main well.

When the car is running the top emulsion bleed effects the low rpm range because air will travel to the
first upper emulsion bleed. This is the cruise mode.

As the engines demand for air increases , due to an increase in throttle opening and rpm, the next bleed
( middle) gets exposed , leaning the mixture with air from the air corrector ( HSAB ).

At the top end of the rev range the fuel drops in the channel to expose the bottom emulsion bleed, adding air to the main well to correct the mixture.

At high rpm , just a few thousands change in the HSAB can have a significant effect on fuel ratio.

[kgb]

No maybe about it, that is the channel I tried describing in the first post. I ignored the idle circuit on purpose to try to avoid confusion, no plan is foolproof.

[rgalajda]

Quote from Tom Vaught: Holley Engineer

In simple terms, Emulsion Holes create air bubbles that lower the fuel density, The lower density fuel "floats" above the normal fuel.
That causes the lower density fuel to have a higher fuel surface level than normal density fuel.

Once the fuel surface level is up to the height of the outlet tube it can flow to the booster. At that point the engine starts to run on the fuel.
At low air flow levels thats the physics behind the Emulsion Circuit. You are using air to make the surface of the fuel closer to the discharge outlet.

At higher flows through the carb the main jet restriction causes a reduction of the liquid level in the well and that lower level uncovers some Emulsion Hole Bleeds. When that happens, the air flow through the bleeds blows the fuel along its path. The amount of "blow thru" is controlled by the Main Air Bleed and the sizing of the various Emulsion Bleeds.

Under Acceleration, when the fuel flow into the bowl causes a lowering of the level (high fuel demand). The pressure on the entrance to the main jet is changed, so the flow rate of the jet is changed and that in turn changes the level of fuel in the main well.

You really have to be "on your game" to be successful when messing with Emulsion Jet changes.

[Christo]

Hi Guys,
I wish there was some photos of some billet 4150 blocks, there use to be lots of pictures of billet metering blocks cut up and explaining a 2 circuit metering block of the main wells and how the emulsion bleeds connect to main wells but i cant find them on the old Taptalk forum. Has anyone got a link i searched the net but no luck.
Thanks guys

[bb79ranch]

Hope this helps: https://www.tapatalk.com/groups/racingf ... 35f6bcd192
This may also help, lots of great knowledge and information from "Shrinker" and "Tuner": https://www.tapatalk.com/groups/britishqueen/