Carter Thermoquads ~ 'More General Information'

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4bbl.
Some comments. Thanks for the info.
- Do not necessarily agree that larger air bleeds that create more emulsion is bad.
Weber carbs have large air bleeds [ air corrector jet ] & make big HP for their size. Atomised fuel burns more efficiently & makes more HP.
- The QJ primary system is different to the TQ, location of air bleeds & number of bleeds, so comparing jet sizing probably doesn't tell us much.
- The only time I have had a TQ bog on the secondaries was when the sec jets were too small; or the AV too loose [ I set at 2 turns ]; or the dashpot was faulty. I also set the AV for 0.050 -0.100" of movement [ kick ] with the dashpot retracted at idle. This initial kick just lets in a more air for the secs to 'grab' & help response.
- The TQ is a brilliantly engineered & sophisticated carb; a lot of thought went into the design & not cheap to make. Better than the POS Holley [ & clones ] & no surprise H copied it, albeit a cheaper version, with the Street Demon.
- The TQ has adjustability for the AV fully open position, something the QJ does not have, making it more versatile when tuning. The sec WOT position is also easier to change than the QJ & the linkage action is more positive.
- I remove all the choke/fast idle linkage mechanism. This leaves holes in the a/horn, which I plug. It also leaves a small opening in the AV. I braze a small piece of steel over this. Without blocking that hole [ which is normally blocked by the choke linkage ] it might cause a lean/bog condition.
- I have enlarged the economizer on a few occasions; also called the Idle Down Channel. There are two body screws roughly inline with the mixture screws, Near each is an alum plug in the a/horn. These can be prised out with a sharp knife. About 35mm in from the front surface is a brass insert. This is the economizer jet. I found they vary from about 048-052", stock. For a big cammed engine, I enlarge them about 0.004".
 
Post 110.
I wouldn't say the TQ idle jets are huge. Some I have measured at 032 & some are 034. Holleys typically 031. The 750/850 Barry Grant street carbs had 033/035 IFRs.
 
I agree, the idle jets are not huge
I said the primary and secondary main jets are huge.
137 and 143 jets on secondary from the factory is huge for an OEM,
it's bigger than what a factory Holley 1150 Dominator came with.
TQ's had 92-100 primary main jets as well. that's very big.
the last 1150 I bought had 92's all the way around, and even THOSE were rich,
because it was a carb with no power valves, so the jets were 6-8 higher than what they should be to start. a Dominator with power valves can run 82-86 jets.
137 or 143 jets are what racers run in alcohol fueled cars, typically 50% higher jetting.
talk to the carb builders who build carbs for $600-$1000 a pop for past 50 years,
when the idle/high speed bleeds in the top get over 70/30 respectively,
and a lot of emulsion jet is used in the metering blocks, i.e. 3-5 per side,
instead of the factory 2 per side, the carb goes nuts.
it becomes like a Binks #7 spray paint gun. turn the air pressure up and down on a spray gun, see which setting pushes more paint out of the tip. if you add a lot of air, there's not enough paint, it goes thin and lean, and you have to open up the fluid setting to mix more paint in to cover. turn the air pressure down, all of a sudden there's too much paint and it's not atomizing, and you have to turn the paint knob in to lean it out.
it's also why a Qjet biggest jet was 78 even if it was on a 500 CID Cadillac, but a Carter TQ had a 104 jet available for primaries. It makes me wonder why?
measuring those air bleeds in the TQ lid, no other carbs I know of, have 2 idle circuit air bleeds in the lid per primary bore. and no other carbs have high speed air bleeds that big either. normal size for a Holley is around 30. the TQ's have 42-52+
the secondary side of the TQ appears to have a normal sized high speed air bleed, 29-38 range.
with all that air bleed on the primary side, the TQ was obviously an emission carb from the get go 1972-onward. This is why the later TQ's are $25 each, but the early 1969-71 CS carbs are $500+ each, if you can even find one for sale.
another tricky factor with a TQ is secondary air valve opening. if the air door is adjusted to open more or less, or open quickly or slower, it affects the mixture dramatically. the air door is like a giant adjustable air bleed. it must be adjusted precisely and specifically for each engine application. the biggest factor is engine size. what works great on a 455, is too quick and bog city on a 350. a bog is a lean condition, too much air too soon.
 
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too much emulsion can fatten up the fuel curve from idle to 40% throttle opening.
too much high speed air bleed can lean the fuel curve beyond 50% throttle opening.
the secondary air bleed is down into the secondary main well, it's filled with fuel, so when air is first sucked into it upon secondary opening, it acts like an accelerator pump, the air pushes the fuel out initially.
many phenoms can occur at sustained WOT in a carburetor, and can be counter-intuitive, i.e. opposite of what's expected, such as the accelerator pump passage can pull air reverse and act like an air bleed. or it can continue on pulling fuel if the check valve or ball doesn't function or is missing.
the idle jet tube can flow air in reverse and become an air bleed, because it's connected to the rear facing idle air bleed down in the primary rod area cavity, in the lid, and the air bleed in the top angled backwards. the diminishing bleed in the venturi prevents this by pulling fuel into the venturi instead, when the idle discharge port/transfer slots turn off at WOT.
on the secondary side, the air bleed tube is just that, an air bleed. but that cross drilled little hole in the bottom of it, below float level, creating 2 little holes, those are emulsion holes.
a TQ carb by design has no primary emulsion holes drilled anywhere just for that specific purpose, like a Holley metering block. the air bleeds themselves emulsify the fuel, in the idle/off idle circuit at part throttle, and inside main metering nozzle passages in the lid.
a carb that's been fiddled with by a tuner, can have too much emulsion, the result will be globs of air and fuel coming out of the nozzles or discharge tubes, in a chaotic manner, instead of a steady atomized stream. like when you turn on your kitchen or bathroom spigot after installing a new hot water heater, and there's air in the pipes, what happens. it sputters, rattles, carries on until all the air is pulled through and discharged. but if there's too much emulsion in the carb circuit, it never goes away. the car falls on it's face, and the tuner is jetting up, down, all over and never can really iron it out. even putting rich jets in, it may act like it's still lean sometimes. the plugs will be black but it acts lean like it's running out of fuel, or vice versa.
Spreadbore carbs like the TQ and Qjet use 2 different delivery systems. The primary has a venturi, the secondary has a discharge tube. Each type reacts different to pressure/vacuum change. The secondary discharge tube senses airflow at 1:1 ratio as pressure/vacuum increases, and fuel flows in direct proportion to the air. The main jet alone will provide the right amount of fuel, with minimum air bleed/emulsion.
The primary booster venturi doesn't flow 1:1, it flows in a straight line as pressure/vacuum increases. The actual airflow curves towards a horizontal flat line. So the booster venturi needs an air correction system/emulsion to allow the booster signal to follow airflow. Emulsified fuel is just the result of the air correction.
 
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C&S Aerosol Billet Carburetor Modifications

C&S Aerosol Billet Carburetor
Modifications Address Basic Flaws
in the 50-Year-Old Conventional Design.

Stock Holley discharge nozzles are very close to the throttle plates. This creates a fuel-distribution problem at part throttle. Throttle plates direct fuel to the center of the intake manifold. This richens center cylinders and leans end cylinders, even if the total mixture was perfect. This reduces potential torque and smoothness (Figure 1).

The new C&S design fixes this problem. Location of the fuel delivery nozzle is raised one-half inch, allowing the mixture to spread before reaching the throttle plates. A greater distribution improvement is gained with a new nozzle design.

The C&S nozzle is machined, not cast; does not "go rich" at high RPM; and has only one-fourth as much fuel-delivery variation from low to high vacuum. It is called an aerosol nozzle because it works on the same principle as an aerosol spray can. As high-velocity air passes over the square-cut tube end, energy is transferred to the liquid, which is broken up into a very fine mist. A portion of fuel travels back the tube to be fogged off at the venturi lip to deliver highly vaporized fuel to the lean side of the throttle plates as shown in Figure 2.
 
another big new "breakthrough" but in reality, just using the secondary discharge tubes from a Qjet or TQ, in all throats of a 4bbl carb. getting rid of the booster venturi cluster altogether also means more airflow. we're seeing a lot of these "breakthroughs" lately...rehash of 50-60 year old technology from the golden age of NHRA/NASCAR racing and musclecars.
like the Street Demon carb made by Holley, with the "new" trap door 3 barrel design, in reality a TQ carb with an early 1963? Holley design secondary from their old trapdoor 4bbl racing carbs made for NASCAR.
most of the engineers and car magazine writers today weren't even alive back then to remember. they did notice an old Holley has the tendency to go rich at high rpm, when jetted dead nuts at idle/off idle...and they can also go lean...
 
pinned out bleeds and idle feed restrictor on early CS 1000cfm TQ lid.
.034" idle feed restrictor
.028" primary high speed air bleed
secondary high speed air bleed- .020" falls in loose and wobbles, .024" won't go in- so it's around .022"
idle air bleed is in usual place facing backward in air bleed/main needle cavity, can't measure it.
CS carb has the diminishing idle air bleed above the booster venturi,
with downward facing main discharge tubes on both primary, secondary
primary nozzles have no air bleeds in the booster venturi or nozzle area
secondary nozzles are not the spray bar type- they have a single open angle cut exit.

comparing the air bleeds in the '72-up 800/850 carbs, to the air bleeds in the '69-'71 CS 850/1000 carbs, a picture emerges:
twice as much or more air bleed size in the later OEM carbs,
and 20-25 bigger jet size in the OEM carbs on secondary.
116 jet in CS1000, 134/143 jets in the OEM's

the hi perf TQcarbs had less jet, smaller air bleeds
the later OEM's have a huge amount of air bleed area in comparison.
maybe too much ?
it would not be difficult to drill/tap the lid of the OEM carbs for removable screw in air bleeds like a Holley, Demon, etc. have
and...the CS carb idle jet could easily be d/t for adjustable idle jets as well.
things that make you go hmmmm.....



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that's where I saw the dashpot vacuum feed fitting with small tiny
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hole...the early CS carbs have it
 
4972 71 340 MT (3512820) 3074 3125 655 1-3/8 6
4973 71 340 AT (3512821) 3074 3125 655 1-3/8 6
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
6144 72 340 AT Export 4095 5137 1950 1-3/8 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
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

interesting specs, just realized
1971 340 had 74 primary/125 secondary jets
1972-73 340 had 95-98 primary/137 secondary jets

ask yourself why would the same motor have a 21-24 sizes bigger primary main jet, and a 22 sizes larger secondary jet, in the 72-up 340 ?? it's just not something we do when tuning a motor for the street, or at the track. it had to be because there is so much more air bleed/emulsion in the later 72-up carbs, they covered it with more jet. not only are the air bleeds 2x bigger in the same places, there's that huge air bleed in the nose of the 72-up primary nozzles, that does not even exist on the pre-72 carbs
 
Few things to cover:
- the orifice size in post 134 looks a little bigger than the one I encountered in the 9333, but similar design. This might explain the smaller sec jets in the CS TQ because that would slow down the dashpot release, make the AV function like a choke blade & richen the mixture.
- the CS TQ has the IFR being fed from the fuel bowl, not from he main well AFTER passing through the m/jet like most other carbs. Only other carbs I am aware of that have this are DCOE & IDA Weber carbs.
- 4500 Hs have 2" sec bores from memory; plus a venturi. TQ/QJ have 2.25" bores & no venturi to cause a restriction. This explains the larger the larger TQ jets, & possibly the small holes in the sec discharge tubes might have an influence on the jet size.
- the top section of the AV on 6000 & 9000 TQs is bent forward. This section was straight on the CS series. Do not know why, but suspect AV/fuel flow action started earlier on the CS.
- QJ/TQ have the booster ring in the primaries, Hs don't. I guess that changes a lot of things in regard to jet & AB size & position.
- the 9333 carb had 101 pri jets. That carb had a horrendous 3/4/1" exh thick heated spacer under it, I think EGR related.
- have seen the C&S carb, it is not new. There is a company that specialises in VW engines that converts Dellorto carbs to a spray bar system with claims of more HP.
- in the TQ/QJ/H dyno test quoted above, it would be interesting to know if all of the TQ tuning tricks were used to maximise output. Only 5 hp difference between the H & the TQ. Could the TQ have done better? On the TQ, these tuning changes could have been tried, but were they: WOT position of the sec blades; being so large they can influence distribution & air flow. WOT position of the AV, which is adjustable. There are a few different AV dashpots available, different spring rates.
 
those are interesting points. there was no outer booster ring on the 1000cfm CS TQ.
but there was an outer booster ring on the 850 CS TQ.

spray bar holes- it appears the Aerosol carb design may use them, to fill the entire carb throat with a more even distribution of fuel.

TQ vs Qjet dyno test- they tried to copy the early CS TQ1000, by modifying a later 72-up TQ model 6322. However, unless the size of the air bleeds in the lid of the 6322 were reduced down to same size as CS TQ carbs, the comparison is not fully valid-

I agree with your speculation, that was my point exactly...

reason: MASSIVE air bleed difference, between early 69-71 CS TQ, and later 72-up OEM TQ. the later 72-up carbs used 2x more air bleed for the primary/secondary main metering circuits, in addition to adding two more air bleeds downstream in the idle circuit that are HUGE. Don't forget about the big air bleed in the top nose of the fuel nozzle, the old CS didn't even have one there.

72-up TQ's need to be richened up. there's no doubt in my mind, if the air bleeds were at least made somewhat smaller, the carb would wake up. I'd start with the same size the 69-71 CS TQ had, then work bigger from there. That extra large idle circuit bleed on the top toward front of carb, that is angled upward/backward, possibly can be blocked completely- because there's still the idle air bleed down in the cavity facing rearward, by the metering rods area. Why have 2 idle air bleeds per side, when the 69-71 CS TQ only had one ?

or....block the idle bleed down in the cavity, and just run the top idle bleed. the top one would be easy to d/t and screw in an adjustable bleed.

The 72-up carbs even SOUND lean, kick them open it sounds like someone left the power brake booster hose off, a hissing sound of air being sucked in, like they're lean. cuz they are lean !! lean as hell.

the Holley being aftermarket HP carb, had no emissions type metering.
the early pre-'75 Qjet, were not as compromised as the 72-up TQ carbs. Qjets were metered relatively rich up to/including 1974. an early 800 Qjet is a mean running mother, I ran them, and rebuilt many. Qjet may be down 50-75cfm compared to a CS TQ, but it's not really enough to matter on the street, or track, everything else being the same. they're just so wickedly responsive !

like this
 
I just noticed, on early 69-71 CS TQ carbs, primary metering rods go directly into the main well, through a vertical passage directly above the jet, the jet is screwed into the lid at bottom of main well- main jet, metering rod, main well all share same stanchion/passage in direct vertical line.
fuel goes past the metering rod directly into the primary discharge tube nozzle, in the booster venturi.
this means, the space around the primary metering rods in the early CS TQ carbs, also serves as an additional air bleed for the primaries. the metering rod guide hole is brass bushed just like an air bleed, to get the proper size- unlike the 72-up carbs, where the metering rod guide holes are just drilled through the aluminum.
The metering rods at that point are .073", the rod guide hole is .076". there's a tad more primary high speed air bleed area there at the interface, no doubt factored in by the engineers back in the day. add that to the primary air bleed tube size of .028" - total high speed air bleed is darn close to .030" then, just like a Holley 4 bbl.
 
4bbl,
Couple of comments. The AFB, AVS & QJ also used two idle air bleeds, so not unique to the TQ.

You brought this up before about the air bleed function of the space around & above the m/rods/main jets. These are not ABs because ABs occur after the fuel has been metered; this is just atmospheric pressure acting on the head of fuel. No different to AP acting on the head of fuel of a Holley jet, except the H jet does not have a m/rod in it restricting flow. The fact that a brass bush was used to guide the m/rod on the CS; maybe be deleted on later models because it was found it was not needed.
 
metering rod to carb lid bushed
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metering rod hole interface. it's a very small air bleed, but an air bleed nonetheless.
 
you are confusing the 72-up carb design, with the earlier CS design. they are not the same.

the 72-up carbs merely have a hole in the lid for metering rod guide, that is above float level, that's only more bowl venting. the metering rod passes through empty space and through the fuel in the bowl, into the jet in floor of bowl.

the CS carbs have the metering rod going directly into main well, attached to the lid. the jet isn't in the floor of the bowl, it's upside down on stanchion, screwed directly onto the bottom of the main well. the metering rod is actually inside the main well. the space around the metering rod is therefore more air bleed. the metering rod doesn't just go through empty air space above fuel level in the bowl, like on a 72-up carb. the dedicated high speed air bleed is alongside this tower, and it bleeds more air into the main metering circuit downstream from the jet/rod.

That gap between the metering rod and bushed guide in lid on the CS carb, tiny as it may be, is still more air bleed, in addition to the dedicated main metering high speed air bleed that's already in the lid. It's splitting hairs but I'm including it anyway- because it's there. It's a critical area, that's why the designers bushed it for tight clearance on the CS carbs. It was not critical on the 72-up carbs.

the idle circuit on a CS carb has its own idle jet and idle well, taking fuel directly from bottom of the bowl, separated from the main jet/main well. it has only one idle air bleed on the lid top, not 2 like the 72-up carb.

looking at bottom of stanchion in pics above, that small brass plug next to the main jet facing downward same direction as main jet, that is the separate dedicated idle well- the idle jet is on opposite side surface of stanchion- the idle air bleed is at top on lid, that angled backward tube in cavity in the corner. the main jet when screwed in, seats itself against the nose of the main well. the idle fuel is drawn into the idle jet, around the cavity surrounding the jet/idle well nose, and out the other side of stanchion, into the idle well, then up the idle well to top. the 2 circuits are separated, just in close proximity to each other.
 
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4bbl,
Yes, I see what you mean now. Do you have a drawing or picture of the hi speed cct on the CS that shows the passages, ABs etc?
 
Bewy said:
4bbl,
Yes, I see what you mean now. Do you have a drawing or picture of the hi speed cct on the CS that shows the passages, ABs etc?
Click to expand...

maybe...somewhere...buried. that's why I posted the pics of the actual carbs, and air bleed locations in both types of carbs. basically any carb has the same circuits/air bleeds. you have to buy one and look at it. ephiphany will strike.
 
here check this out

Carter TQ carb tuning - now with improved 'computer technology'...

So below are 3 separate runs:
1) baseline run, stock setups as follows:
ROD = 2110
JET_P = 95
JET_S = 137
AIRBLEED = 65

2) RUN2, moved to richer rods resulting in 8% more fuel @ cruise and 5% more @ WOT (primary side only), used a smaller idle air bleed, looking to bleed off less idle signal and cause the idle circuit to pull more fuel
ROD = 1996
JET_P = 95
JET_S = 137
AIRBLEED = 54

3) RUN3, kept the richers rods but moved to a much smaller idle air bleed, result was an instant 'HOLY [Edited by Farley's]'...now we've got idle and idle mixture screws actually work!!!...basically with the roughly 1/2 sized air bleed (size wise not surface area) I am bleeding off much less signal now and therefore causing a lot more fuel to be fed into the carb idle circuit...nearing the Carter TQ idle holy grail here...
w00t.gif

ROD = 1996
JET_P = 95
JET_S = 137
AIRBLEED = 37
 
notice in his 3rd tune/test, all he did was reduce air bleed by .017"
rods/jets stayed the same. presto- magic.
that's how fine an adjustment we're talking about. pin drills.

think of it this way-

changing jets/rods, reading plugs, is hot rodding 101.

getting into the various air bleeds, is carb guru stuff. like what Barry Grant, Nickerson, Jet Performance did on Holleys, Qjets, etc. that takes it to the next level.

a lot can be done by swapping a 400/440 carb, onto a 318/340/360 engine, because the bigger engine was usually metered richer at the factory due to its sheer size. but not the other way around. put a 318 carb on a 440, it'll may end up blowing flames out of the carb, too lean.

that's where 440 Cuda's old posts were so handy, you could choose a rich metered carb from his "good" list. that was a great starting point. he understood the system that was in place in the 1970's.
 
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4bbl.

I have two 850 CS TQs, bought one new in the 1970s, push in jets. Mate recently bought an 850 & 1000.
The C&S aerosol carbs have been around for years, probably 20 or more. I used to see them advertised in CT magazine. The theory looks good, but if they really
work well, why are not more in use? Especially Nascar type racing.
 
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