[Region Warrior]

Chiphead has good info.

Took 2 hrs on a supposed expert Holley guy set up a 850 for a buddy's 455 with 230/240 something cam with torque 2 intake.
Everything wrong.
Fuel level in bowls 3/4" high.
Pump levers set over tight fuel leak at idle.
Primaries open above idle slots.
Needed 5 jets lower both bowls.
Same guy told him 28* max timing.

[chiphead]

Originally Posted by Region Warrior

Chiphead has good info.

Took 2 hrs on a supposed expert Holley guy set up a 850 for a buddy's 455 with 230/240 something cam with torque 2 intake.
Everything wrong.
Fuel level in bowls 3/4" high.
Pump levers set over tight fuel leak at idle.
Primaries open above idle slots.
Needed 5 jets lower both bowls.
Same guy told him 28* max timing.

it seems like the guy was trying to get it to provide more fuel. Raising the level richens it up everywhere and helps the mains pull over faster. Too much transfer slot means it needed secondary plates open a smidge and more idle fuel. That would allow closing the primaries down.

This is why big name carb builders charge so much. It seems like regular enthusiasts have no idea how a carb really works. Any time a carb runs rich, the power valve or main jets get blamed every time. If it runs lean, its the accel pump shot. Its nuts.

I found the Holley secret decoder ring on some website in the corner of the internet. I was searching for emulsion bleed tuning and found it. The curves show you what orifice to change to move the fuel curve where you want it. I've tested this and it works. Add the factors of fuel pressure, fuel level and aircleaner restriction and you can make a holley 4150/4160 work how you want.

Check this out.

[HWYSTR455]

The standard 4150s generally come with .097 needle & seats, and will cause lean conditions with more 'thirsty' combos. People throw jets at it and it turns into a pig.

I think the out of box double pumper come with .110 needle and seats, even that can be an issue.

IMO, go right to a .130 or .150, there's no downside really, and since there's more area to seal, it seals better, you can run more psi too.

A lot of people think they need 50cc pumps too, and that's not always the case. Everyone starts playing with cams, diff squirters, and it can quickly get out of hand.

Emulsion bleed tuning really is more useful in drag or circuit racing, when you have some gear more towards one side of the spectrum and specific demands. For 'general' street strip stuff, you can get by with the out of box bleeds.


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[chiphead]

Originally Posted by HWYSTR455

Emulsion bleed tuning really is more useful in drag or circuit racing, when you have some gear more towards one side of the spectrum and specific demands. For 'general' street strip stuff, you can get by with the out of box bleeds.


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I want to mention this part, since it's part of the wackiness we see in modern carbs. For decades, the stock Holley carbs on production cars like Ford 390s had a small number of small emulsion bleeds in the metering block. Those were either 2 vertical bleeds into the main well, or the bleed tubes that are inside the main well. The upper hole right below fuel level controls pullover, and the hole about 1/2 down from that helps shape the fuel curve once the mains get going. Those 2 holes, along with the high speed air bleed and the main jet, control the main circuit fuel curve.

There were a few cases where adding a 3rd hole between the two would add fuel at part throttle, heavy load conditions for racing. Adding emulsion air to the main well lifts fuel and makes it richer, especially at low to moderate venturi airflow. The fuel is lifted by the bubbles, so it takes less venturi signal to flow fuel. This makes the curve richer until venturi draw gets stronger, and then the air through the bleed system starts to displace the fuel and the delivery leans out. The rate of fall in the wells depends on the size of the main jet. Smaller the jet, the faster the fuel falls and uncovers additional bleed(s). This is how the jets, emulsions and the HSAB add or remove fuel from the main circuit.

Then the aftermarket figured more is better, and now you have 3, 4, 5 emulsion holes in the main well of aftermarket billet metering blocks. "Out of the box" bleeds are now out to lunch for a mild street motor.

This usually results in rich fueling from 2300-4000 RPM, when on the mains at part throttle. Then when you got to WOT, the mixture leans out too much as the air displaces the fuel in the main well. You can't add enough jet or power valve to richen it back up at WOT, without rolling coal at 3000 RPM.

The solution is set the top hole and the 3rd hole at .028" and block all the others. That recreates the old-school setup from the 1960s. That usually helps get the main circuit back under control. Then sizing the main jet, HSAB and the fuel level starts the mains at the correct time and keeps it from curving rich/lean at WOT. You see this if you follow the curves from the chart.

The most interesting thing is look at the effect of the HSAB. (Some call it a MAB, I call it a HSAB and I aim to kill yo with it- Karl from Sling Blade)

Conventional wisdom is that the larger the high speed bleed, the later the mains start and leaner it is everywhere. However, a larger bleed will blow air through the emulsion well and the main well at low venturi signals. Those bubbles lift the fuel up to the booster and now its flowing fuel. This will actually start the mains EARLIER and make it RICHER, until the system starts to displace fuel in the wells with bleed air. At that point, it swings violently lean, cuz it taint got no gas in it. Its all about the total amount of air available from the HSAB, the size AND location of the emulsions in relation to the fuel level in the well and how hard the booster is pulling on the well.

[Formulajones]

The most emulsions I've seen lately on aftermarket carbs is 3. I got my hands recently on an ATM and it only has 2.

The problem with that carb is how insanely lean it is on tip in and light throttle to the point the engine gets into a stumble it doesn't want to recover from . Very difficult to just cruise around town.
Im talking AFR's going from 13.0 at idle to pegging the gauge at 20 with any light tip in. It's crazy how much I've fattened all kinds of circuits up to cover that hole. Forget about AFR readings, lol

[chiphead]

Have you relocated the IFRs to the lower positions? That usually helps a lot with the condition you describe.

Most all newer holley clones locate the Idle Feed Restrictions in the high location, above liquid fuel. In a lot of cases, you can tune the idle mixture to be correct, but when you get into the transfer slots, it goes lean or erratic. Moving the IFRs to the lower location under the fuel level really helps stabilize the idle circuit fueling.

I never really tuned a mechanical secondary carb until I bought my current '67. It had a QuickFuel 750-HR double pumper, and it ran like chit. I did the typical stuff but it was still fat and lazy.

I searched the internet high and low, Yellowbullet, The HAMB, Don Terrel's speedtalk, the Mopar boards, racingfuelsystems.com, here on PY, etc trying to figure out how to tune it. I bought a couple of the older Holley tuning books. Nobody covers the HSAB or the emulsions in deep detail. Its nuts how quiet everybody is on those critical parts of a holley carb. Tom V, Kenth and a few of the carb guys here were very helpful on explaining the advanced tuning approaches. Its in a thread somewhere here on PY.

Finally I found posts copied from the old Innovate Forum back in 2011 or so. There were some guys named Klaus and Tuner that explained two-phase flow in detail, and the cutaways on the below website helped me understand it.
Sorry for the long-winded posts, but I tend to brain-dump on carb threads now. Somebody in the future will come across this and it'll save them some time.

https://garage.grumpysperformance.co...59/#post-56233