Billet Metering Blocks

Have no experience with that, just theory, and boy that is getting deep into a carb...

IFR's (Idle Feed Restriction), PVCR's (Power Valve Channel Restrictions),

Emulsification Bleeds, size, number of them, and elevation locations, Kill Bleeds,

Main Jets, Air Bleeds, Main and Idle, Primary and Secondary, shew...

Have you checked that at idle the Primary Transfer Slots are not over exposed ?

And if so, close down the Primary Idle Speed Screw and open up the Secondary Idle Speed Screw?

Supposedly what you describe -can be- caused by over exposed Primary Transfer Slots, but not always.

( EDIT ) As mentioned, this is getting deep into carb operation theory...

Something I found and will post below suggest what I typed here is ? wrong or backwards ?

But I am not sure...

A minuscule delay in the Main Boosters coming online could also cause it.

Smaller Main Air Bleeds will quicken Boosters coming online,

or changes to the Metering Block Emulsification Bleed configuration will also,

raising the level where emulsification air is first introduced into the metering block

should richen the mixture and quicken when the Main Boosters come online.

All just theoretical gobbally gook, but sounds like a fun tuning challenge to me Geek

Edited by PHAT69AMX - Jun/01/2019 at 2:46pm

Link to a Short YouTube Burnout Video

Thanks bwamx !

Ok, more deep carb operation theory about Air Bleeds & Booster Timing... Google found this for me.

Objective, original poster Grey Ghost with his E85 Carb looks to eliminate jump in stumble...

Thinking is to quicken Primary Booster Discharge.

There is a LOT here to read, but there is a LOT to it...

And it can be tough to follow...

I first posted to quicken Booster Discharge RAISE where Emulsion Air comes in...

The below text suggest the opposite -IF- I am reading it correctly...

LESS BLEED AIR on TOP of fuel in the Emulsion Wells quickens Booster Start-Up ?...

Introduce Emulsion Bleed Air LOWER in the well quickens Booster Start-Up ?...

This is from the old Innovate Forum.

The numbered paragraphs 1 thru 4 below sum it up.

In the thread “750 Holley Carb Help” Klaus made this statement, “On carbs it's very important that the correct two-phase flow gets established during emulsion. Otherwise you will see RPM dependency of AFR.” Thank you Klaus, but forgive me if I see your remark as a profound understatement. Incorrect two-phase flow is at the root of all this aggravation. People who have drill bits but don’t know why to use them have been molesting innocent carburetors for a long time. Now some of them are in charge of the manufacture of new carbs and they think they have improved them by using larger drill bits to make the air bleed and “emulsion” orifices. I guess the guys that engineered the original carburetors on the old muscle cars were pretty stupid or they would have “improved the emulsion” 40 or 50 years ago when they had their chance. After all, they had the awesome power of the single-point ignition system at their disposal, they shouldn’t have been afraid of a little soot.

It is well documented that introducing air into the main well encourages low signal flow and can encourage or discourage high signal flow. The natural characteristic of a plain jet and nozzle (no air) is to get richer as airflow increases. The purpose of the air bleed system is to modify that behavior to accomplish a constant (or the desired) air/fuel ratio over as wide a range of airflows as possible. The particular ratios for power and cruise are realized by the selection of jet and rod or jet and auxiliary jet (power valve channel). The purpose of air bleeds is not to emulsify but to accomplish the correct fuel delivery. Emulsion is just a beneficial side effect.

What I’m going on about here is Klaus’ remark about “correct two-phase flow”. That is the description of a fluid flow that is made up of a liquid and a gas flowing together in the same conduit. As the ratio of gas to liquid increases (more gas, less liquid), at some point the gas bubbles coalesce from many small ones into a few big ones and the flow starts to “slug” and become erratic. The carburetor nozzle spits like a garden hose with air in it when there is too much “emulsion” air.

An emulsion of air and fuel has reduced density, surface tension and viscosity compared to fuel alone. This increases the flow of fuel considerably, particularly in low-pressure difference operation, at low throttle openings or lower engine speeds. Just how much of an increase (richer) is dependent upon where and how much air is introduced into the fuel flow.

Mainly, what must be understood is that because the fuel discharge nozzle connects the venturi to the main well, whatever the low pressure (vacuum) is in the venturi, it is also the pressure in the main well. The air bleed is in the carb air horn or somewhere else where it is exposed to essentially atmospheric pressure, which is higher than the venturi pressure. This pressure difference causes air from the air bleed to flow through the emulsion system into the main well and to the nozzle. The flow of air can have very high velocities, approaching sonic in some orifices. The airflow literally blows the fuel toward and through the nozzle. A larger main air bleed will admit more air to the emulsion system and that can increase or decrease fuel flow to the engine. The size, number and location of the other air holes in the emulsion system, the size of the main well flow area, the size of the nozzle and the specific pressure difference at the moment are the determining factors. The ratios of air volume to fuel volume to flow area, with the air volume's expansion with the venturi velocity induced pressure reduction being the key. The bubbles expand as the pressure drop increases with airflow. Suck on an empty balloon to experience the effect.

The fuel flow through the main jet is the result of the pressure difference between the atmospheric pressure in the float bowl and the venturi air velocity induced vacuum acting on the nozzle and the main well. The venturi vacuum in the well is reduced (the pressure is raised) by the "air leak" from the air bleed. This reduces the pressure difference that causes the flow through the main jet. If the air bleed were big enough, the pressure in the well would be the same as in the float bowl and no fuel would flow. Think about drinking through a soda straw with a hole in it above liquid level. Bigger hole, less soda. Suck harder, not much more soda. Big enough hole, no soda. This is the means by which the emulsion system can "lean it out on the top end". Incidentally, the vacuum that lifts water up a soda straw is in the most sensitive operating range for emulsion systems.

It is in the lowest range of throttle opening, at the start of main system flow, that the effect of adjusting the introduced emulsion air (and its effect in increasing the main fuel flow) is most critical. Small changes can have large and sometimes unexpected or counter-intuitive consequences. The goal is to seamlessly blend the rising main flow with the declining idle/transition system fuel delivery to accomplish smooth engine operation during opening of the throttle in all conditions, whether from curb idle or any higher engine speed. The high speed and load mixture correction is usually easily accomplished, in comparison.

The vertical location of the bleeds entering the main well influences the fuel flow in the following ways:.

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.

2 ) Orifices at float level increase low range (early throttle opening) fuel flow by carrying fuel with the airflow to the nozzle.

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.

4 ) The "emulsion holes" influence is greatest at low flows and the "main air bleed" has most influence at high flows.

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 phenomenon of critical flow is what limits the total air flow through an orifice and allows tuning by changing bleed size.

Essentially, the emulsion effect will richen the low flow and the air bleed size, main well and nozzle restrictions will control the increase or reduction of high flow. Again, the desired air/fuel ratio is the primary purpose of the bleed system. "Improved emulsion" is an oxymoron if the modification of air bleeds to "improve emulsion" results in an incorrect air/fuel ratio in some range of engine operation. Correct proportioning of all the different bleeds (and, of course, the idle, transition and power circuits) will give the correct air/fuel ratios over the total range of speeds and loads and a flat air/fuel ratio characteristic at wide open throttle.

Edited by PHAT69AMX - Jun/01/2019 at 3:14pm

Link to a Short YouTube Burnout Video

Short and sweet... reduce or eliminate emulsion orifices that are above float level...

Desired result being quickened primary booster discharge...

Link to a Short YouTube Burnout Video

Author	Message Topic Search Topic Options Post Reply Create New Topic Printable Version Translate Topic
Grey Ghost Members Profile Send Private Message Find Members Posts Add to Buddy List AMC Apprentice Joined: Oct/11/2009 Location: Route 66 Il. Status: Offline Points: 158	Post Options Post Reply Quote Grey Ghost Report Post Thanks(0) Quote Reply Topic: Billet Metering Blocks Posted: May/29/2019 at 9:43pm
	I've got a 4150 Pro Systems carb that I did an E85 conversion to 5 or 6 years ago. the car is mainly bracket raced but was staring to get a little erratic, during normal service I found that the original cast metering blocks were starting to corrode in the channels so I purchased the Quick Fuel E85 metering blocks. To date the car has been more consistent than it has ever been, my issue is that in the transition from off idle to WOT the engine seems to hesitate and surge I did not have this issue before the swap. Does any one have any experience tuning metering blocks I cannot find any info online and the directions supplied don't give any information. BTW I do not run a power valve. Thanks.
	Lets go racing!

PHAT69AMX Members Profile Send Private Message Find Members Posts Add to Buddy List AMC Addicted Joined: Jul/07/2007 Location: West Virginia Status: Offline Points: 5919	Post Options Post Reply Quote PHAT69AMX Report Post Thanks(0) Quote Reply Posted: May/31/2019 at 1:42pm
	Have no experience with that, just theory, and boy that is getting deep into a carb... IFR's (Idle Feed Restriction), PVCR's (Power Valve Channel Restrictions), Emulsification Bleeds, size, number of them, and elevation locations, Kill Bleeds, Main Jets, Air Bleeds, Main and Idle, Primary and Secondary, shew... Have you checked that at idle the Primary Transfer Slots are not over exposed ? And if so, close down the Primary Idle Speed Screw and open up the Secondary Idle Speed Screw? Supposedly what you describe -can be- caused by over exposed Primary Transfer Slots, but not always. ( EDIT ) As mentioned, this is getting deep into carb operation theory... Something I found and will post below suggest what I typed here is ? wrong or backwards ? But I am not sure... A minuscule delay in the Main Boosters coming online could also cause it. Smaller Main Air Bleeds will quicken Boosters coming online, or changes to the Metering Block Emulsification Bleed configuration will also, raising the level where emulsification air is first introduced into the metering block should richen the mixture and quicken when the Main Boosters come online. All just theoretical gobbally gook, but sounds like a fun tuning challenge to me Edited by PHAT69AMX - Jun/01/2019 at 2:46pm
	Link to a Short YouTube Burnout Video

bwamx Members Profile Send Private Message Find Members Posts Add to Buddy List AMC Apprentice Joined: Mar/27/2012 Location: CT Status: Offline Points: 143	Post Options Post Reply Quote bwamx Report Post Thanks(1) Quote Reply Posted: Jun/01/2019 at 12:02pm
	Ok long story short, the best thing you can do is to document all the sizes of the passages on your original metering blocks. Idle feed, emulsion and so on. PVCR doesn't matter as you stated that you are not running a power valve. Then compare everything on the new blocks. PHAT is correct on his statements , as this might not be just one change. How many emulsion holes are on the original blocks ? I see that the Quick Fuel blocks I looked up have 4 , Yours probably had 2-3 as a guess. Also look and see were the Idle feed restrictions are, on the bottom of the block or the top. I had to move them down to the bottom on my gas quick fuel blocks. The transition slots also play a big deal , and you might have to re tailor the accelerator pump shot . See the link below about the idle feed restriction location, and search the forum for the rest. https://www.tapatalk.com/groups/racingfuelsystems/viewtopic.php?f=31&t=18 - https://www.tapatalk.com/groups/racingfuelsystems/viewtopic.php?f=31&t=18 Great forum and lots of info, plenty to read. Also more : http://www.yellowbullet.com/forum/showthread.php?t=490296 - http://www.yellowbullet.com/forum/showthread.php?t=490296 I've spent lots of time on 2 different sets of Holley's on my crossram . Just remember to do 1 change at a time and document everything. Also a AFR meter is a big tuning tool . Hope this helps Bob

PHAT69AMX Members Profile Send Private Message Find Members Posts Add to Buddy List AMC Addicted Joined: Jul/07/2007 Location: West Virginia Status: Offline Points: 5919	Post Options Post Reply Quote PHAT69AMX Report Post Thanks(0) Quote Reply Posted: Jun/01/2019 at 3:12pm
	Thanks bwamx ! Ok, more deep carb operation theory about Air Bleeds & Booster Timing... Google found this for me. Objective, original poster Grey Ghost with his E85 Carb looks to eliminate jump in stumble... Thinking is to quicken Primary Booster Discharge. There is a LOT here to read, but there is a LOT to it... And it can be tough to follow... I first posted to quicken Booster Discharge RAISE where Emulsion Air comes in... The below text suggest the opposite -IF- I am reading it correctly... LESS BLEED AIR on TOP of fuel in the Emulsion Wells quickens Booster Start-Up ?... Introduce Emulsion Bleed Air LOWER in the well quickens Booster Start-Up ?... This is from the old Innovate Forum. The numbered paragraphs 1 thru 4 below sum it up. In the thread “750 Holley Carb Help” Klaus made this statement, “On carbs it's very important that the correct two-phase flow gets established during emulsion. Otherwise you will see RPM dependency of AFR.” Thank you Klaus, but forgive me if I see your remark as a profound understatement. Incorrect two-phase flow is at the root of all this aggravation. People who have drill bits but don’t know why to use them have been molesting innocent carburetors for a long time. Now some of them are in charge of the manufacture of new carbs and they think they have improved them by using larger drill bits to make the air bleed and “emulsion” orifices. I guess the guys that engineered the original carburetors on the old muscle cars were pretty stupid or they would have “improved the emulsion” 40 or 50 years ago when they had their chance. After all, they had the awesome power of the single-point ignition system at their disposal, they shouldn’t have been afraid of a little soot. It is well documented that introducing air into the main well encourages low signal flow and can encourage or discourage high signal flow. The natural characteristic of a plain jet and nozzle (no air) is to get richer as airflow increases. The purpose of the air bleed system is to modify that behavior to accomplish a constant (or the desired) air/fuel ratio over as wide a range of airflows as possible. The particular ratios for power and cruise are realized by the selection of jet and rod or jet and auxiliary jet (power valve channel). The purpose of air bleeds is not to emulsify but to accomplish the correct fuel delivery. Emulsion is just a beneficial side effect. What I’m going on about here is Klaus’ remark about “correct two-phase flow”. That is the description of a fluid flow that is made up of a liquid and a gas flowing together in the same conduit. As the ratio of gas to liquid increases (more gas, less liquid), at some point the gas bubbles coalesce from many small ones into a few big ones and the flow starts to “slug” and become erratic. The carburetor nozzle spits like a garden hose with air in it when there is too much “emulsion” air. An emulsion of air and fuel has reduced density, surface tension and viscosity compared to fuel alone. This increases the flow of fuel considerably, particularly in low-pressure difference operation, at low throttle openings or lower engine speeds. Just how much of an increase (richer) is dependent upon where and how much air is introduced into the fuel flow. Mainly, what must be understood is that because the fuel discharge nozzle connects the venturi to the main well, whatever the low pressure (vacuum) is in the venturi, it is also the pressure in the main well. The air bleed is in the carb air horn or somewhere else where it is exposed to essentially atmospheric pressure, which is higher than the venturi pressure. This pressure difference causes air from the air bleed to flow through the emulsion system into the main well and to the nozzle. The flow of air can have very high velocities, approaching sonic in some orifices. The airflow literally blows the fuel toward and through the nozzle. A larger main air bleed will admit more air to the emulsion system and that can increase or decrease fuel flow to the engine. The size, number and location of the other air holes in the emulsion system, the size of the main well flow area, the size of the nozzle and the specific pressure difference at the moment are the determining factors. The ratios of air volume to fuel volume to flow area, with the air volume's expansion with the venturi velocity induced pressure reduction being the key. The bubbles expand as the pressure drop increases with airflow. Suck on an empty balloon to experience the effect. The fuel flow through the main jet is the result of the pressure difference between the atmospheric pressure in the float bowl and the venturi air velocity induced vacuum acting on the nozzle and the main well. The venturi vacuum in the well is reduced (the pressure is raised) by the "air leak" from the air bleed. This reduces the pressure difference that causes the flow through the main jet. If the air bleed were big enough, the pressure in the well would be the same as in the float bowl and no fuel would flow. Think about drinking through a soda straw with a hole in it above liquid level. Bigger hole, less soda. Suck harder, not much more soda. Big enough hole, no soda. This is the means by which the emulsion system can "lean it out on the top end". Incidentally, the vacuum that lifts water up a soda straw is in the most sensitive operating range for emulsion systems. It is in the lowest range of throttle opening, at the start of main system flow, that the effect of adjusting the introduced emulsion air (and its effect in increasing the main fuel flow) is most critical. Small changes can have large and sometimes unexpected or counter-intuitive consequences. The goal is to seamlessly blend the rising main flow with the declining idle/transition system fuel delivery to accomplish smooth engine operation during opening of the throttle in all conditions, whether from curb idle or any higher engine speed. The high speed and load mixture correction is usually easily accomplished, in comparison. The vertical location of the bleeds entering the main well influences the fuel flow in the following ways:. 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. 2 ) Orifices at float level increase low range (early throttle opening) fuel flow by carrying fuel with the airflow to the nozzle. 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. 4 ) The "emulsion holes" influence is greatest at low flows and the "main air bleed" has most influence at high flows. 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 phenomenon of critical flow is what limits the total air flow through an orifice and allows tuning by changing bleed size. Essentially, the emulsion effect will richen the low flow and the air bleed size, main well and nozzle restrictions will control the increase or reduction of high flow. Again, the desired air/fuel ratio is the primary purpose of the bleed system. "Improved emulsion" is an oxymoron if the modification of air bleeds to "improve emulsion" results in an incorrect air/fuel ratio in some range of engine operation. Correct proportioning of all the different bleeds (and, of course, the idle, transition and power circuits) will give the correct air/fuel ratios over the total range of speeds and loads and a flat air/fuel ratio characteristic at wide open throttle. Edited by PHAT69AMX - Jun/01/2019 at 3:14pm
	Link to a Short YouTube Burnout Video

Grey Ghost Members Profile Send Private Message Find Members Posts Add to Buddy List AMC Apprentice Joined: Oct/11/2009 Location: Route 66 Il. Status: Offline Points: 158	Post Options Post Reply Quote Grey Ghost Report Post Thanks(0) Quote Reply Posted: Jun/02/2019 at 10:19pm
	bwamx, I will compare metering blocks, but as far as accelerator pump shots go's I think I am past that point during the burn out and the issue occurs during a light cruise back to the pits the car surges like it has erratic fuel pressure
	Lets go racing!

PHAT69AMX Members Profile Send Private Message Find Members Posts Add to Buddy List AMC Addicted Joined: Jul/07/2007 Location: West Virginia Status: Offline Points: 5919	Post Options Post Reply Quote PHAT69AMX Report Post Thanks(0) Quote Reply Posted: Jun/02/2019 at 10:31pm
	Short and sweet... reduce or eliminate emulsion orifices that are above float level... Desired result being quickened primary booster discharge...
	Link to a Short YouTube Burnout Video