Carter Thermoquads ~ 'More General Information'

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Carter Thermoquad

1975 '400/240 HP' Engines

TQ-9008


Primary ............. 1 1/2" {1.500"} ........ Venturi = 1.186"
Secondary ......... 2 1/4" {2.250"}

Primary Jet ......... .098
Secondary Jet ..... .143"

Metering Rod ....... 1965 {.069" Economy ~ .061" Mid-Range ~ .045" Power}

Needle and Seat .... .0935"

CFM Rating ........ 787 CFM's

'400' Intake Manifold ..... #3830949

The #9008 was designed to run 'lean' at Mid-Range.
 
These carbs(T/Q ,pre smog..) are a bear to tune, but once set are absolutely reliable. I am a hardcore Holley guy,still like these carbs.
 
No doubt Bomber. Once in there excellent carbs street, street/strip carbs.
Normally they can be found in rebuildable condition cheaply. The cost of cleaning and a kit for a very flexible unit far out weighed the cost of a new carb. In the past when I first got into them, for under $90, I would have it up and running.
 
These carbs(T/Q ,pre smog..) are a bear to tune, but once set are absolutely reliable. I am a hardcore Holley guy,still like these carbs.

Correct,

An early Thermoquad is not for the 'Average Joe'..........

You need some patience, and experience to dial them in.

The 1972 thru 1974 'solid fuel metering' Carbs are the most desired,
for bolt-on performance units.

1972 Series
* 6138S > 340/240 HP {M/T}
* 6139S > 340/240 HP {A/T}
* 6140S > 400/255 HP {M/T}
* 6141S > 400/255 HP {A/T}

1973 Series
* 6318S > 340/240 HP {M/T}
* 6319S > 340/240 HP {A/T}
* 6320S > 400/260 HP {M/T}
* 6321S > 400/260 HP {A/T}
* 6324S > 440/280 HP {A/T}

1974 Series
* 6452S > 360/245 HP {M/T}
* 6453S > 360/245 HP {A/T}
* 6456S > 400/250 HP {M/T}
* 6457S > 400/250 HP {A/T}
* 9015S > 440/275 HP {A/T}

Next choice, would be the 1975 Carbs with the {IES} and {TPS} contraptions,
which both can be removed.
 
I wrote it yet a few pages before:

I have a 6394S Thermoquad, this number is not listed above, but should be standard on 1972 340s AT for export.

I can - if wanted - post pictures of this special type of Thermoquad, but I cannot tell anything about the specialities of this carb or the differences to the 6139S type.
 
Heeyyy.... It's Marvin, the Martian....Are you planning, to blow up Earth today?... (Lol)
 
I wrote it yet a few pages before:

I have a 6394S Thermoquad, this number is not listed above, but should be standard on 1972 340s AT for export.

I can - if wanted - post pictures of this special type of Thermoquad, but I cannot tell anything about the specialities of this carb or the differences to the 6139S type.

6394S ....... {1973 / 1974} > '340' Export {A/T}

Primary ........... 1 3/8" {1.375} .... Venturi 1.063"
Secondary ....... 2 1/4" {2.500"}

Primary Jets ...... .095"
Secondary Jets ... .137"

Metering Rod ...... 1950 {.068" Economy ~ .057" Mid-Range ~ .040" Power}

Needle and Seat ... .0935"

CFM Rating ...... 737 CFM's
---------------------------------------------------------------------------------------

Note > These 'export' Thermoquad's were designed to run 'lean' in the
Mid-Range level, but to run on the 'rich side' under heavy-throttle.
 
Correct,

An early Thermoquad is not for the 'Average Joe'..........

You need some patience, and experience to dial them in.

The 1972 thru 1974 'solid fuel metering' Carbs are the most desired,
for bolt-on performance units.

1972 Series
* 6138S > 340/240 HP {M/T}
* 6139S > 340/240 HP {A/T}
* 6140S > 400/255 HP {M/T}
* 6141S > 400/255 HP {A/T}

1973 Series
* 6318S > 340/240 HP {M/T}
* 6319S > 340/240 HP {A/T}
* 6320S > 400/260 HP {M/T}
* 6321S > 400/260 HP {A/T}
* 6324S > 440/280 HP {A/T}

1974 Series
* 6452S > 360/245 HP {M/T}
* 6453S > 360/245 HP {A/T}
* 6456S > 400/250 HP {M/T}
* 6457S > 400/250 HP {A/T}
* 9015S > 440/275 HP {A/T}

Next choice, would be the 1975 Carbs with the {IES} and {TPS} contraptions,
which both can be removed.

Above ^^^^^^^ the good list.
 
old thread but worth reviving, question:
the list of "good" solid fuel metered TQ carbs,
why is #6090 not in the list ? It's a factory 400 cid carb,
with the larger 1.5" primaries, 850cfm
how bad can it be ?
question to 69 cuda 440,
is your list based on only the carbs you found, and used yourself ?
YES, I would exclude any carbs marked "CA", as they are California emissions.
no doubt leaner, with early emissions controls.
but what's wrong with all the other 72-74 TQ carbs ?
any of them should work, when dialed in with jets, rods, etc.
what makes some of them undesirable and not on your list ?
there's many pre-'75 TQ to choose from. what makes them good or bad ?
any should work. I'd prefer the 1.5" primary for extra 50cfm, no ?
the 6090 is the earliest 850 they made with solid fuel metering.
one would assume it has the least amount of emissions bs on it,
and would be metered the richest from the factory,
being these carbs were progressively metered leaner with passing years,
as the Federal/State emissions standards were tightened.
please explain. because if you haven't actually TRIED every single pre-'75 carb,
how can you recommend only that short list you posted ?
finally, I find it hard to believe, that any production TQ,
has more potential than an early Competition Series TQ,
because the early CS series were designed for racing, no holds barred.
they have the richest metering of any made, period.
I obtained many of them, and kept all the 1000cfm units, and one 850 center section. Both jets being in the top lid, eliminates the possible O ring sealing issue in the base, that the later TQ's experienced.

Model Application Pri. Sec. Rod Bore Kit
4846S Competition Series 331 341 615 1-1/2 8
4846SA Competition Series 3080 3116 615 1-1/2 8
4847S Competition Series 331 341 616 1-1/2 8
4847SA Competition Series 3089 3116 616 1-1/2 8
4972 71 340 MT (3512820) 3074 3125 655 1-3/8 6
4973 71 340 AT (3512821) 3074 3125 655 1-3/8 6
6090 72 400 AT F (3614139) 4095 5137 1937 1-1/2 1
6138 72 340 MT F (3614122) 4095 5137 1940 1-3/8 1
6139 72 340 AT F (3614123) 4095 5137 1940 1-3/8 1
6140 72 400 MT F (3614138) 4095 5137 1939 1-1/2 1
6144 72 340 AT Export 4095 5137 1950 1-3/8 1
6165 72 400 MT CA (3614172) 4095 5137 1938 1-1/2 1
6166 72 400 AT CA (3614173) 4095 5137 1938 1-1/2 1
6318 73 340 MT F (3698327) 4098 5137 1962 1-3/8 1
6319 73 340 AT F (3698328) 4098 5137 1966 1-3/8 1
6320 73 400 HP MT F (3698332) 4098 5137 1965 1-1/2 1
6321 73 400 HP AT F (3698333) 4098 5137 1966 1-1/2 1
6322 73 440 & Truck AT F (3698334) 4098 5125 1966 1-1/2 1
6324 73 440 HP AT F (3698336) 4098 5125 1966 1-1/2 1
6339 73 340 MT CA (3698339) 4098 5137 1962 1-1/2 1
6340 73 340 AT CA (3698340) 4098 5137 1966 1-1/2 1
6341 73 400 MT CA (3698342) 4098 5137 1965 1-3/8 1
6342 73 400 AT CA (3698343) 4098 5137 1966 1-3/8 1
6394 72-73 340 AT Export - - - 1-3/8 1
6410 73 440 & Truck AT CA (3698319) 4098 5125 1966 1-1/2 1
6411 73 440 HP AT CA (3698329) 4098 5125 1966 1-1/2 1
6446 M-440 Chrysler Marine (3698397) - - - 1-1/2 1
6452 74 360 HP MT F (3751433) 4098 5143 1962 1-1/2 1
6453 74 360 HP AT F (3751434) 4098 5143 2005 1-1/2 1
6454 74 360 HP MT CA (3751435) 4098 5143 1962 1-1/2 1
6455 74 360 HP AT CA (3751436) 4098 5143 2005 1-1/2 1
6456 74 400 HP MT F (3751439) 4098 5143 1966 1-1/2 1
6457 74 400 HP AT F (3751440) 4098 5143 1966 1-1/2 1
6459 74 400 HP AT CA 4098 5143 1966 1-1/2 1
6460 74 440 AT F early (3751443) 4098 5137 1966 1-1/2 1
6461 74 440 AT CA early (3751444) 4098 5137 2005 1-1/2 1
6462 74 440 HP AT F early (3751445) - - - 1-1/2 1
6463 74 440 HP AT CA early (3751446) - - - 1-1/2 1
6488 74 360 AT CA early (3751451) 4098 5143 1966 1-1/2 1
6489 74 400 AT F early (3751452) - - - 1-1/2 1
6496 74 400 AT CA 4098 5143 2005 1-1/2 1
6503 74 400 AT Export - - - 1-1/2 1
 
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69 Cuda 440 has passed away. He is now listed as a “Legendary member” for this reason.

One of the reasons he lists the carbs he did was lack of emission items and design on the carb. Also, the lady at would be very long. To include every last desirable carb would be a big task. Missing one or two is easy.

old thread but worth reviving, question:
the list of "good" solid fuel metered TQ carbs,
why is #6090 not in the list ? It's a factory 400 cid carb,
with the larger 1.5" primaries, 850cfm
how bad can it be ?
question to 69 cuda 440,
is your list based on only the carbs you found, and used yourself ?
what's wrong with all the other 72-74 TQ carbs ?
any of them should work, when dialed in with jets, rods, etc.
what makes some of them undesirable and not on your list ?
there's many pre-'75 TQ to choose from. what makes them good or bad ?
any should work. I'd prefer the 1.5" primary for extra 50cfm, no ?
the 6090 is the earliest 850 they made with solid fuel metering.
one would assume it has the least amount of emissions bs on it,
and would be metered the richest from the factory,
being these carbs were progressively metered leaner with passing years,
as the Federal/State emissions standards were tightened.
please explain. because if you haven't actually TRIED every single pre-'75 carb,
how can you recommend only that short list you posted ?

Model Application Pri. Sec. Rod Bore Kit
4846S Competition Series 331 341 615 1-1/2 8
4846SA Competition Series 3080 3116 615 1-1/2 8
4847S Competition Series 331 341 616 1-1/2 8
4847SA Competition Series 3089 3116 616 1-1/2 8
4972 71 340 MT (3512820) 3074 3125 655 1-3/8 6
4973 71 340 AT (3512821) 3074 3125 655 1-3/8 6
6090 72 400 AT F (3614139) 4095 5137 1937 1-1/2 1
6138 72 340 MT F (3614122) 4095 5137 1940 1-3/8 1
6139 72 340 AT F (3614123) 4095 5137 1940 1-3/8 1
6140 72 400 MT F (3614138) 4095 5137 1939 1-1/2 1
6144 72 340 AT Export 4095 5137 1950 1-3/8 1
6165 72 400 MT CA (3614172) 4095 5137 1938 1-1/2 1
6166 72 400 AT CA (3614173) 4095 5137 1938 1-1/2 1
6318 73 340 MT F (3698327) 4098 5137 1962 1-3/8 1
6319 73 340 AT F (3698328) 4098 5137 1966 1-3/8 1
6320 73 400 HP MT F (3698332) 4098 5137 1965 1-1/2 1
6321 73 400 HP AT F (3698333) 4098 5137 1966 1-1/2 1
6322 73 440 & Truck AT F (3698334) 4098 5125 1966 1-1/2 1
6324 73 440 HP AT F (3698336) 4098 5125 1966 1-1/2 1
6339 73 340 MT CA (3698339) 4098 5137 1962 1-1/2 1
6340 73 340 AT CA (3698340) 4098 5137 1966 1-1/2 1
6341 73 400 MT CA (3698342) 4098 5137 1965 1-3/8 1
6342 73 400 AT CA (3698343) 4098 5137 1966 1-3/8 1
6394 72-73 340 AT Export - - - 1-3/8 1
6410 73 440 & Truck AT CA (3698319) 4098 5125 1966 1-1/2 1
6411 73 440 HP AT CA (3698329) 4098 5125 1966 1-1/2 1
6446 M-440 Chrysler Marine (3698397) - - - 1-1/2 1
6452 74 360 HP MT F (3751433) 4098 5143 1962 1-1/2 1
6453 74 360 HP AT F (3751434) 4098 5143 2005 1-1/2 1
6454 74 360 HP MT CA (3751435) 4098 5143 1962 1-1/2 1
6455 74 360 HP AT CA (3751436) 4098 5143 2005 1-1/2 1
6456 74 400 HP MT F (3751439) 4098 5143 1966 1-1/2 1
6457 74 400 HP AT F (3751440) 4098 5143 1966 1-1/2 1
6459 74 400 HP AT CA 4098 5143 1966 1-1/2 1
6460 74 440 AT F early (3751443) 4098 5137 1966 1-1/2 1
6461 74 440 AT CA early (3751444) 4098 5137 2005 1-1/2 1
6462 74 440 HP AT F early (3751445) - - - 1-1/2 1
6463 74 440 HP AT CA early (3751446) - - - 1-1/2 1
6488 74 360 AT CA early (3751451) 4098 5143 1966 1-1/2 1
6489 74 400 AT F early (3751452) - - - 1-1/2 1
6496 74 400 AT CA 4098 5143 2005 1-1/2 1
6503 74 400 AT Export - - - 1-1/2 1
 
69 Cuda 440 has passed away. He is now listed as a “Legendary member” for this reason.

One of the reasons he lists the carbs he did was lack of emission items and design on the carb. Also, the lady at would be very long. To include every last desirable carb would be a big task. Missing one or two is easy.

sorry to hear that. I'm 60 now and mortality is tapping me on the shoulder as well...
he probably just never ran into a 6090...understood...
 
Years ago, I obtained many of these pre-'75 TQ carbs, including 8-10 of the early 4846/4847 CS series, and the later CS. I'd generally avoid the later model CS series made after 1974. If you can get the early CS series from 1969-72, they are the best for all out performance. Many have seen hard use and may be somewhat worn, damaged. Jets for them are hard to find, and pricey- but I managed to find enough years ago to have a personal supply. At the time the Buick GS guys had most of them- and were parting with their carbs, parts, jets to upgrade to Demons, Holley HP, XP, etc.- because carb technology jumped ahead quite a bit after 2000. So I'd get all that stuff with their carbs. According to the GS guys, the 1000 cfm worked, because it slowed down the velocity, allowing the mixture to turn the sharp corners of the flat workbench-like Buick factory intake manifold, thereby getting more into the engine, and making more power.
My own best list is any pre-'75 TQ---with the CA California Emissions, export carbs, idle enrichment carbs as a last resort. Having said that you can de-emission those as well with some extra work, but it may involve drilling out/replacing idle feed holes, air bleeds. So I'd stick with the others for simplicity, and go with the 1-1/2" primaries for 50cfm more capacity, only use the 1-3/8" primaries for smaller engines below 350cid, if at all. The smaller double venturi will tend to nozzle drizzle with a big cam at idle, because it has so much velocity. I've drilled the early CS carb for more idle bypass air with a big cam.
The early pressed jet carbs can be used, but if you pull the original jets, you'll have to work at resealing them with O-rings, sealer, or tap the holes for screw in jets- and risk damaging the jets or carb trying to pull the jets out. The carb lid must be carefully lightly heated, or boiled in water, to remove them if stuck fast. and/or soaked in penetrating oil. If you obtain a number of early CS jets, and they are multiples of the same size, you can drill them for in between sizes using a drill index. There's nothing wrong with a Marine or IH truck carb, they often have rich metering for lugging loads, and work good for performance cars as well.
 
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I'd like to add one more important fact:
In every reference database about TQ carbs, they mention early carbs being air metered, and later carbs being solid fuel metered, then another thread elsewhere on the net states the difference is, solid fuel metered TQ carbs add air after the fuel is discharged from the nozzle. air metered TQ carbs add air before the fuel is discharged.
that is simply incorrect, and somewhat misleading. they both add air before the fuel is discharged, using air bleeds in the air horn, in the same place. the later carbs just add more air at the nozzle as well.
I have both types of carburetors, looked at them closely. there is only one slight difference between the 2 types.

1. the early carburetors pre-'72 have 8 air bleeds in the top lid. 2 are in the primary bores above the venturis, one per side in the front corners, pointing inward above the nozzles. these can flow both ways. air can be pulled into idle circuit, or fuel can be pulled out at certain velocities into the venturi. there's also one idle air bleed on each side near the primary metering rods, in corners of the top cavity, exposed.
there are 2 more per each side under the plates where the metering rods go down through the lid in that same cavity. if you remove the plates you can see them. 1 is for primary main metering, 1 is for secondary main metering. they are the small tiny ones going straight down. so there is a total of 8 air bleeds in the early CS carbs. there are no air bleeds in the nozzles themselves.

2. the later '72-up carburetors have those same 8 air bleeds, but the idle air bleeds are not in the primary bores, instead they're relocated to the venturi, a large air bleed in the nozzle itself. but it's not mixing the air with the fuel AFTER the fuel exits the nozzle. it's putting air into the nozzle and mixing it with fuel INSIDE THE NOZZLE. there is still an aerated/emulsified mixture exiting the nozzle, just like the early CS carbs- only it is emulsified to a higher degree. this is the same thing Barry Grant did to the Holley design when he released the Demon carbs- he added extra emulsification bleeds to the metering blocks. where Holley only had 2 bleeds per barrel in the block itself, BG had up to 5 per side.

3. the holes in the primary rod guide holes in the top of the carb on the early CS models, go directly down into the main jet well. when those rods are pulled up out of the holes at WOT, the space between the primary metering rods and guide holes also becomes an air bleed. any holes above float level into metering passages become air bleeds of sorts. and holes below float level are fuel metering. on some designs a fuel metering hole may be uncovered at WOT, and become an air bleed at higher rpm- and vice versa.

this is nothing out of the ordinary. the TQ is an improved Qjet carb design, improved with more airflow, 2 floats, 2 needle valves, 2 larger fuel bowls, and will generally support a somewhat higher HP output than a Qjet-at least on paper- due to increased fuel/air supply and flow. if you ran a 1972-up Mopar in NHRA SuperStock, you must run a TQ per the rules- how bad can they be ? the Qjet also has air bleeds at the nozzle, just like the TQ, the Qjet had them from day one. and they also do quite well making 600-700HP+ in SuperStock no problem.

the correct description of the pre-'72 TQ carbs would be, "without nozzle/booster venturi air bleeds".
the later 1972-up carbs do not add air to the fuel after the fuel discharges from the nozzle. it adds air before that point just like any other carburetor does with the air bleeds in the same position- what it does is, adds more air AT THE NOZZLE internally, before the a/f mixture is discharged.

take a look at the 2 types closely with a bright light, and remove the upper plates, and look closely in the bores, etc. inspect the nozzles, there is an air bleed on top, discharge hole on bottom. as the fuel enters the tip of nozzle, it pulls air through the upper hole, both air and fuel exist the bottom together. the point of all this, air was introduced prior to the nozzle, far upstream, by the air bleeds at top of air horn, near the primary metering rods.

Holley high performance racing carbs typically have no air bleeds at the nozzle, just hole for fuel to discharge from. neither does the secondaries on the Qjet or TQ.
 
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Great old thread thanks for resurrecting it. I love old Black magic or Mr ugly:thankyou:
 
old thread but worth reviving, question:
the list of "good" solid fuel metered TQ carbs,
why is #6090 not in the list ? It's a factory 400 cid carb,
with the larger 1.5" primaries, 850cfm
how bad can it be ? ...

See post # 16. I've run a 6090s TQ and 72 400 intake on a street HP 383 and loved it. Got 18 mpg highway to boot.
 
Is it possible to get a few pictures up of the air bleeds and other things your talking about? This would be absolutely great for everybody to learn from.

I'd like to add one more important fact:
In every reference database about TQ carbs, they mention early carbs being air metered, and later carbs being solid fuel metered, then another thread elsewhere on the net states the difference is, solid fuel metered TQ carbs add air after the fuel is discharged from the nozzle. air metered TQ carbs add air before the fuel is discharged.
that is simply incorrect, and somewhat misleading. they both add air before the fuel is discharged, using air bleeds in the air horn, in the same place. the later carbs just add more air at the nozzle as well.
I have both types of carburetors, looked at them closely. there is only one slight difference between the 2 types.

1. the early carburetors pre-'72 have 8 air bleeds in the top lid. 2 are in the primary bores above the venturis, one per side in the front corners, pointing inward above the nozzles. these can flow both ways. air can be pulled into idle circuit, or fuel can be pulled out at certain velocities into the venturi. there's also one idle air bleed on each side near the primary metering rods, in corners of the top cavity, exposed.
there are 2 more per each side under the plates where the metering rods go down through the lid in that same cavity. if you remove the plates you can see them. 1 is for primary main metering, 1 is for secondary main metering. they are the small tiny ones going straight down. so there is a total of 8 air bleeds in the early CS carbs. there are no air bleeds in the nozzles themselves.

2. the later '72-up carburetors have those same 8 air bleeds, but the idle air bleeds are not in the primary bores, instead they're relocated to the venturi, a large air bleed in the nozzle itself. but it's not mixing the air with the fuel AFTER the fuel exits the nozzle. it's putting air into the nozzle and mixing it with fuel INSIDE THE NOZZLE. there is still an aerated/emulsified mixture exiting the nozzle, just like the early CS carbs- only it is emulsified to a higher degree. this is the same thing Barry Grant did to the Holley design when he released the Demon carbs- he added extra emulsification bleeds to the metering blocks. where Holley only had 2 bleeds per barrel in the block itself, BG had up to 5 per side.

3. the holes in the primary rod guide holes in the top of the carb on the early CS models, go directly down into the main jet well. when those rods are pulled up out of the holes at WOT, the space between the primary metering rods and guide holes also becomes an air bleed. any holes above float level into metering passages become air bleeds of sorts. and holes below float level are fuel metering. on some designs a fuel metering hole may be uncovered at WOT, and become an air bleed at higher rpm- and vice versa.

this is nothing out of the ordinary. the TQ is an improved Qjet carb design, improved with more airflow, 2 floats, 2 needle valves, 2 larger fuel bowls, and will generally support a somewhat higher HP output than a Qjet-at least on paper- due to increased fuel/air supply and flow. if you ran a 1972-up Mopar in NHRA SuperStock, you must run a TQ per the rules- how bad can they be ? the Qjet also has air bleeds at the nozzle, just like the TQ, the Qjet had them from day one. and they also do quite well making 600-700HP+ in SuperStock no problem.

the correct description of the pre-'72 TQ carbs would be, "without nozzle/booster venturi air bleeds".
the later 1972-up carbs do not add air to the fuel after the fuel discharges from the nozzle. it adds air before that point just like any other carburetor does with the air bleeds in the same position- what it does is, adds more air AT THE NOZZLE internally, before the a/f mixture is discharged.

take a look at the 2 types closely with a bright light, and remove the upper plates, and look closely in the bores, etc. inspect the nozzles, there is an air bleed on top, discharge hole on bottom. as the fuel enters the tip of nozzle, it pulls air through the upper hole, both air and fuel exist the bottom together. the point of all this, air was introduced prior to the nozzle, far upstream, by the air bleeds at top of air horn, near the primary metering rods.

Holley high performance racing carbs typically have no air bleeds at the nozzle, just hole for fuel to discharge from. neither does the secondaries on the Qjet or TQ.
 
Good info here but disagree with point #3 in post #92.
The guide holes for the met rods, whether CS or production TQs are not air bleeds.
Air bleeds occur AFTER the fuel has been metered by the main jet.
In the above scenario, the fuel has not passed through the m/jet. The air is atmospheric pressure acting on the fuel above the jet & fuel will flow when the pressure at the discharge point is lower than atmospheric.
 
I stand corrected....the primary needles not being sealed tightly against their guides, would alter the venting to atmospheric pressure- not the emulsion/air bleed.
 
the early '69-'71 TQ's had downward angled nozzles.

the later '72-up TQ carbs, was add upward angled nozzles with air bleeds in the top nose, to allow air to pass through the top of the nozzle and mix with fuel. same as a Qjet.

but...the air metered and solid fuel metered both have air bleeds in the lid, in almsot the exact same place. that the solid fuel metered does, is merely move some bleeds close to/into the nozzle itself. for more fine control, for emissions. that's why Holleys 4bbl and the old CS carbs don't use solid fuel metering, they were not emission carbs, but strictly racing/performance carbs. that's also why Holleys get such lousy mileage, and were always pig rich (laughter...)but I still like my Holleys...they have their place.

the best illustrations for the difference, are the BBD 2-barrel on Mike's Carb Parts site. notice the "solid fuel metering" still has an air bleed facing forward in the nozzle cluster horizontally, in addition to an air bleed in the top nose of the upward facing nozzle, with a fuel discharge hole in the bottom of the nozzle.

basically solid fuel metering adds many more AIR BLEEDS, closer to the cluster/nozzle, which has the effect of leaning out the mixture, and adding emulsion to the mixture, and a finer control of the nozzle discharge.
Barry Grant was famous for doing the same thing with the Holley design, in his Demon carbs. instead of 2-3 emulsion air bleeds per barrel, there were 5-6 air bleeds per barrel. the idle/high speed air bleeds in the top were also larger than standard Holley bleeds for the same size carburetor. this can be a 2-edged sword in some applications. it delays primary activation, adds emulsions, and leans it, but then richens it at the top end. the air rushing into all those open air bleeds at WOT, has the effect of pushing the fuel out of the nozzles at WOT and high rpm. so it can create a top end rich condition.

BBD Identification

Air Bled & Solid Fuel

Air Bled

The air bled circuit used prior to 197 4 has an emulsion tube or vent tube that extends downward into the high speed well. This tube mixes air with the fuel before it leaves the high speed well. The air bled design always uses “down hill” nozzles. The air bleed in the high speed circuit also serve as-an anti-percolator passage.

bbd-air-bled.jpg

Solid Fuel

The solid fuel design, 1974 and ‘later, takes solid fuel from the high speed well and bleeds air into the circuit at the top through the extended vent tubes located in the cluster, closer to the tip of the nozzle. The solid fuel design always uses “uphill” nozzles and gives a closer calibration to meet the emission standards and also serves as an anti-percolator passage.

bbd-solid-fuel.jpg
 
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the air bleeds above the venturi in the early CS series carbs, were "diminishing air bleeds", Qjets also used them on some models as well, they'll bleed air, but also discharge fuel at WOT high velocities to supplement primary main metering.

diminishing-well-bleeds.png


Diminishing Well Bleeds
Some solid fuel models use diminishing well bleeds. This bleed is subjected to venturi pressure changes that follow engine load conditions. They serve as self-adjusting air bleeds and at or near the wide-open throttle, could deliver fuel.

The two center holes are the pump discharge windows and also the air bleed to prevent pump pull over. A pump pullover is when gas is coming out of the discharge when the accelerator pump isn’t being activated.
 
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