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post #16 of 33 (permalink) Old 02-17-2017, 09:42 AM
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Originally Posted by THE EVIL TW1N View Post
Tuning a carb is very complicated, but doable. It depends how far you are willing to dig to do it right.

There are basically two circuits on the typical Holley (low speed and high speed). As was stated before, the idle resides on the low speed circuit.

If you wanted to lean out part throttle, you will need to run a smaller IFR. Most aftermarket Holley metering blocks run .036 IFR's. I found a .032 or so is more acceptable, assuming you have decent vacuum. But that only has a limited result in leaning out the part throttle. You don't want to go too small with the IFR because your carb pulls fuel from the transition slots during cruise and very light throttle, and those would run lean too with the change.

There is more to be done to lean out the part throttle. I'm assuming you have set your main jets for a good WOT AFR (~12.7-13.1), and a correct power valve for your vacuum (and capped rear power valve). The next step would be to run larger power valve restrictors so that you could run a smaller main jets on the front metering block. This way you still have the same overall jet needed for 3/4 throttle - WOT, but a smaller leaner jet for soft part throttle.

Having said all that, I doubt you have adjustable metering blocks.
Well that isn't true. There is an idle circuit, a transition circuit, a main circuit, a power circuit and of course a choke circuit.That doesn't included the accelerator curcuit which piggy backs on the others. So, not as simple as you say.
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post #17 of 33 (permalink) Old 02-17-2017, 11:11 AM
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https://www.amazon.com/Holley-Carbur...buretor+tuning

The first edition of this back in the mid late 60s is were I started learning about carbs suggest reading it several times

I still pull it out now and then to refresh my memory as it describes how some circuits work a bit different than others in different style carbs.

s far as a Holley style idle circuit goes the idle mixture is actually controlled by the Idle Air Bleeds (IAB). The air pulled through these mixes with fuel pulled through Idle Fuel Restrictions (IFR). The Idle Feed Screws adjust the amount of the emulsion (the mixture of air and fuel from the IAB and IFR. [The idle mixture screw in most carbs dosent really adjust the mixture just the amount].
The mixture is realy closest to being correct when the idle feed screw set at best a half turn in or out compromises the idle. Idle fuel comes out a small hole below the throttle blade KNOWN AS THE Idle Feed. Just above the Idle Feed Hole is the Idle Transfer Slot. About .030 to .045 of that slot should be showing between the blade and the idle feed hole. The main jet dosent come into play in the idle circuit unless main jet sizes change by 10 sizes or more.

The idle circuit transfers into the main circuit around 2000 RPM give or take in most cases. IABs have some control as to when the idle circuit transfers to the main circuit so changing their sizes affects the transition point.
The IFR has the most effect on the idle fuel emulsion as it measures the fuel like the main jet. The IAB makes changes in much smaller steps.
Big issue except in certain carbs drilling out these orifices have to be drilled out or filled in then redrilled or in dome cases a piece of guitar wire used, holes drilled and tapped for size 6 or 8 brass set screws to be drilled out and used as jets inplace of the brass inserts.
Or a carb such as the Quick Fuel carbs that have removable jets in all metering orifices.
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post #18 of 33 (permalink) Old 02-17-2017, 12:41 PM
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Originally Posted by turbo2256b View Post
"....... Or a carb such as the Quick Fuel carbs that have removable jets in all metering orifices.
Also good to know: the mid range & higher end Holley's such as the Street HO series have additional tuning ability, like replaceable air bleeds. But it bears pointing out, tht unless your engine is greatly modified, the basic Holley will work just fine. Extra adjustability doesn't always mean superior performance.




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Last edited by zray; 02-17-2017 at 12:45 PM.
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post #19 of 33 (permalink) Old 02-17-2017, 01:10 PM
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Four corner idle, substituting air bleeds, etc. are all things that are more
the bailiwick of someone tuning on a dyno or who has access to a wide
band A/F meter (like an Innovate) at the very least.
Without those things you're just guessing at fuel curve.

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post #20 of 33 (permalink) Old 02-17-2017, 01:25 PM
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Quote:
Originally Posted by GT289 View Post
Four corner idle, substituting air bleeds, etc. are all things that are more
the bailiwick of someone tuning on a dyno or who has access to a wide
band A/F meter (like an Innovate) at the very least.
Without those things you're just guessing at fuel curve.
tHESE DAYS IT IS but BACK IN THE MID 60s UNTIL ABOUT 10 YEARS AGO NEVER USED an AF gage. Just read plugs, vacuum gauge , temp gauge, ETs, fuel mileage, throttle response, etc.
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post #21 of 33 (permalink) Old 02-17-2017, 03:18 PM
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Quote:
Originally Posted by GT289 View Post
Four corner idle, substituting air bleeds, etc. are all things that are more
the bailiwick of someone tuning on a dyno or who has access to a wide
band A/F meter (like an Innovate) at the very least.
Without those things you're just guessing at fuel curve.
Absolutely ! If I hadn't been relying on my AEM a/f gauge it would have taken days, not hours to get the right tune on my Paxton's and Weber.

Z

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post #22 of 33 (permalink) Old 02-17-2017, 04:04 PM
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Quote:
Originally Posted by Claudemiro View Post
Well that isn't true. There is an idle circuit, a transition circuit, a main circuit, a power circuit and of course a choke circuit.That doesn't included the accelerator curcuit which piggy backs on the others. So, not as simple as you say.
You can word it anyway you want and try to be cute about it, but generally, Holley's are considered to be 2 circuit carbs. The Dominators are considered 3 circuits. So yes it is true.

Straight from Holley:

https://www.holley.com/products/fuel...ors/dominator/

1969 MaCh 1 - CHP 427w 10.8:1 comp
TFS 205cc 11R heads || Victor Jr. intake || 950 Holley HP carb || 110* 236/240 .573/.594 hyd roller cam || 1 3/4" ceramic coated headers || 3" exhaust, x-pipe || 14" 6 piston front and 13" 4 piston rear Wilwood brakes || T56 Magnum || SPEC 2+ hydraulic clutch || 9" Detroit Locker || 3.70 gears || MSD 6AL-2 || PST Aluminum DS || many more.

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post #23 of 33 (permalink) Old 02-17-2017, 08:02 PM
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[url] The Idle Feed Screws adjust the amount of the emulsion (the mixture of air and fuel from the IAB and IFR. [The idle mixture screw in most carbs dosent really adjust the mixture just the amount of emulsion].
.

Really huh? You don't have it right. The fuel mixture screws ACTUALLY do control the amount of fuel that comes through the idle circuit. There is no magic here. And emulsion is not a noun, it's not a thing per se. And emulsion tube controls the air flow in small amounts, to control overly rich conditions as venturi vacuum increases. This causes more fuel to enter the stream and in some cases, the mixture is too rich. An emulsion tube allows extra air to mix with the fuel. It's still an air fuel mixture, regardless. It's not something special, doesn't get a new name. I know you have a hot engine in your car and that's cool, but your carburetor information is not correct.
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post #24 of 33 (permalink) Old 02-17-2017, 08:03 PM
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Quote:
Originally Posted by THE EVIL TW1N View Post
You can word it anyway you want and try to be cute about it, but generally, Holley's are considered to be 2 circuit carbs. The Dominators are considered 3 circuits. So yes it is true.

Straight from Holley:

https://www.holley.com/products/fuel...ors/dominator/
There's nothing cute about the facts. I presented the facts, not dreamland, just the facts.
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post #25 of 33 (permalink) Old 02-17-2017, 08:11 PM
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Originally Posted by Claudemiro View Post
There's nothing cute about the facts. I presented the facts, not dreamland, just the facts.
And so did I. I'm not saying you were wrong in listing the different circuits within the two main circuits the carb operates with. But when I stated they were considered two circuit carbs (which they are - FACT - Holley refers to them as two circuit carbs), you oddly had no problem trying to discredit my post. There is no need for that, especially when the information I posted was fact and true to begin with. It makes no sense, you were making a point to just create an argument out of nothing.
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1969 MaCh 1 - CHP 427w 10.8:1 comp
TFS 205cc 11R heads || Victor Jr. intake || 950 Holley HP carb || 110* 236/240 .573/.594 hyd roller cam || 1 3/4" ceramic coated headers || 3" exhaust, x-pipe || 14" 6 piston front and 13" 4 piston rear Wilwood brakes || T56 Magnum || SPEC 2+ hydraulic clutch || 9" Detroit Locker || 3.70 gears || MSD 6AL-2 || PST Aluminum DS || many more.

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post #26 of 33 (permalink) Old 02-17-2017, 10:25 PM
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Take it to a dyno shop and have then tune the carb and ignition timing.

66 coupe, '93 Fox seats, Three point belts, 289, 500 Cfm, Weiand, Hipo manifolds, duel exhaust, T5 trans, Pro 5.0 shifter, 3.40 open, KH front disc, Porterfield R4-S pads, 1" front sway bar, Shelby drop, Spring perch relocation, Shelby quick steer, GT progressive coils (1/2 coil cut), 4.5 leaf mid-eye, KYB Gas-A-Just front & GR-2 rear, Export brace, Monti-Carlo bar, Sub-frame connectors, Performance alignment (+3.5 caster/-.5 camber), 16x7 wheels, 215/55/16 & 225/55/16 BFG G-force

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post #27 of 33 (permalink) Old 02-17-2017, 11:14 PM
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Take it to a dyno shop and have then tune the carb and ignition timing.
A dyno will tune for WOT, but a street tune is still necessary. Unless all you do is WOT runs with the car.

1969 MaCh 1 - CHP 427w 10.8:1 comp
TFS 205cc 11R heads || Victor Jr. intake || 950 Holley HP carb || 110* 236/240 .573/.594 hyd roller cam || 1 3/4" ceramic coated headers || 3" exhaust, x-pipe || 14" 6 piston front and 13" 4 piston rear Wilwood brakes || T56 Magnum || SPEC 2+ hydraulic clutch || 9" Detroit Locker || 3.70 gears || MSD 6AL-2 || PST Aluminum DS || many more.

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post #28 of 33 (permalink) Old 02-18-2017, 10:42 AM
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Originally Posted by Claudemiro View Post
Really huh? You don't have it right. The fuel mixture screws ACTUALLY do control the amount of fuel that comes through the idle circuit. There is no magic here. And emulsion is not a noun, it's not a thing per se. And emulsion tube controls the air flow in small amounts, to control overly rich conditions as venturi vacuum increases. This causes more fuel to enter the stream and in some cases, the mixture is too rich. An emulsion tube allows extra air to mix with the fuel. It's still an air fuel mixture, regardless. It's not something special, doesn't get a new name. I know you have a hot engine in your car and that's cool, but your carburetor information is not correct.
This shows exactly what I stated. Fuel comes through the IFR, air comes through the IAB mixes togeather commonly called an emulsion then the amount of the emulsion is at idle metered into the carb/engine by the idle mixture screw.
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post #29 of 33 (permalink) Old 02-18-2017, 10:54 PM
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Carburetor Tuning the Scientific Way

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post #30 of 33 (permalink) Old 02-18-2017, 10:57 PM
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Originally Posted by turbo2256b View Post
This shows exactly what I stated. Fuel comes through the IFR, air comes through the IAB mixes togeather commonly called an emulsion then the amount of the emulsion is at idle metered into the carb/engine by the idle mixture screw.
Sorry, I didn't learn from just a picture. I had lots of training. Trust me, I'm right. And the noun is an "emulsion tube". The"tube" makes it a noun.
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