Street / Strip Carter TQ jetting configurations....

For those of you running the almighty Carter TQ (Thermoquad), street/strip configuration (so not a dedicated strip/bracket car - but I'd still love to hear about your setup), can you share what jet/rod/idle screw/air door settings you're running?

I have a 9800 electric choke carb here, also have the luxury of a wide assortment of jets and rods (prior kit searches and years of accumulating spare TQs for parts...LOL), however, try as I might I'm having a hard time getting to a suitable combination.

So in short, this is a small block (360 build), TQ on a Perfomer RPM intake with adapter plate, currently running the following setup:

RODS = 2005
IDLE MID WOT
0.065 0.055 0.040

PRIMARY JET = 100
SECONDARY JET = 143
METERING TREE = 1.5 turns from bottomed out
IDLE MIX SCREWS = 4 turns out
AIR DOOR TENSION = 2.5 turns from door just touching the airhorn
AIR DOOR OPENING = .750" measured between dimple and back throttle bore

I have my Innovate LM1 wide-band O2 sensor to monitor the AFR. Street manners wise this combo seems great, idle @800RPM is about 14-14.4 AFR, seems sort of lean, but gives great throttle response, not loading up in gear and at idle. This combination pulls the highest vacum, adding more idle mix turns richens it up and vac drops and it loads up when left in gear for extended amount of time. About 13-13.3 during cruise, and about 12.5 in power step. However, as my secondaries kick-in the ratio will stabilize around high 12s, so 12.7-12.8, but consistently I see some crazy drops to as low as 10s...which implies incredibly rich!!!

Don't get me wrong, the car seems to love it...best throttle response and seems to make good power...but to what extent should I be worried about the rich/low AFR?

I've calibrated (and re-calibrated just to be sure) the O2 sensor, seems to check out fine.

So what are you guys out there running?

hi, I remove the spring from under cross bar. let metering rods ride with the throttle. they can jump up at low vac and cause rich condition also, I set the metering rod bar to make prim jetting. my combo is .095 /.098 pri, 154 sec, 2004 rods. .775 door opening. going down the track , mine shows 12.3 to 12.4 at wide open throttle. no spikes. this is on a 340 with stock intake
these are from mopar race manual.

Hmm...good point...I'm going to try this approach. I have in the past tried different springs, eventually I found one that was weaker then stock.


Yes, I understand that...but I'm looking for the actual settings that work for you. So, given all the literature I have, and the countless posts it looks like that "1-turn from bottomed out" setting is the factory starting point. I had mine set up to 1.5 turns, seemed to work OK.


Why are you running the different primary jet sizes? I have the MP books here as well, and noticed that, my guess was due to fuel distribution and runner design. Since I'm running Perfomer RPM intake I decided to just stick with matched sizes.

Back when I tried a TQ on my drag car I had jumping metering rods too. The trick was to find a spare set of springs and clip a coil off at a time til they no longer danced with the vacuum pulses.

i used a TQ on my 440 setup in my stick Challenger. ran .104 pri, .147 sec. 1997 metering rod. use to run 12.0's with it. couple 11.9 runs at 116mph. i have a different setup now on the car. miss the old TQ. i always loved peoples reaction when i opened the hood.


***Edit***

oh forgot. i put 4 turns on the secondary door spring after it's level with the top. any less and it lived up to it moniker, thermobog.

i used to run a tq on my former 340 in a dart hangten. ran 12.70s through the mufflers. i always ran it with stock jetting on the primaries and concentrated my efforts on the accelerator pump and secondary circuits. i used a shooter drilled to .028 in. and moved the acc. rod in the hole closest to the center of the carb on the lever for more pump shot. it allowed me to set the trap door tension to only 1 1/2 turns without bogging on the leave. i used .815 in. on the trap door opening with .156 secondary jets (drilled). i think yours is too rich at wide open throttle probably because your trap door is closed too much. something to try. by the way, mine was the small primary bore size ( 1 3/8) .

"Idle mixture screws 4 turns out."
Wow! So you have larger primary jets?

The TQ's normally are a difficult thing on the secondary side. I don't think you will find perfection.

I have done the same.

Can't comment on the secondary side jetting as I actually had to drill mine out to get the fuel mixture where I wanted it to be. After 25 years don't recall where its at. I did drill out the spray bars too on the secondary side and removed the "baffle" there after I had one fail and get ingested into the motor.

Car ran faster than ever. I'd laugh as I removed parts of the carburetor the car would just keep going faster and faster..

another thing that comes to mind when tuning tq`s. the carb must be vented anytime it is under full-throttle. if the vent is not operative on your carb, it will be impossible to tune. if so, remove the small rubber that closes the vent inside the carb. you would stay surprised the difference it makes. good luck.

good to know, thanks!

the stock intake has two size plenums.one is short other is deep.
I have .098 on deep side. .095 on smaller side. my plugs look better. like I stated, fuel curve is flat. no spikes!! the sec air bleeds have been soldered and drilled to about 1/2 their size. this richens up jetting the motor sees, without sucking the bowls dry.

I'm running a .100 primary jet right now, and by 4 turns I mean full turns off of the screws just being seated. Normally with all my other combinations I have to run at least 6 turns to get any sort of decent/stable idle.

The ideal meetering rod @ idle turned out to be the 2005 (75-2005 - 0.065,0.055,0.040), but past idle it was just too darn rich at cruise.

So I moved to 2144 now (75-2144 - 0.069,0.061,0.050) which with the same primary jetting gave me a pretty decent all around performance and my AFR is around the 14.1 @ idle, 13.5 @ cruise and about 13.3 @ WOT.

So I want the idle/off-idle performance of the 2005 rod but primary main and high-speed performance of 2144 rod. Ideally I'd like to run the 2005 rod for the primary side (pulling 8-9" of vac @ 800RPM is great with my cam) but need to go a bit leaner on the jets, so I will try a move to 0.095 jet, while on the secondary I'll go up to 0.149, measure it and maybe drill a set out to 0.154, or more, given that my air-door openning distance right now is on the smaller side.

Hmm...OK, worth a try, I have the vent currently plugged with a cap on the vent tube only because I didn't feel like running a vent line to the purge carnister (one less vac line in the engine bay, kept it cleaner), but I had never realized this might be the implication. Good call!!!

I would have considered the primary side lean at more than 3 turns. But what ever works for your combo.

The suggestion on the secondary side and drilling out the spray bars should help out. This mod is normally seen on pretty modified engines making some real decent power. Good luck. I'm keeping tuned in on this one.

hi, no need to drill out sec bars. besides , you have to remove them to do it!!they are swedged in tight. this is for all out race engines. resize sec air bleeds will do you more good and easier to do. you still use same sec jets. also, I raise and lower the metering bar to affect mixture on pri side.

Can you post a picture as to where the secondary air bleeds are located?

hi, I don't have way to post pictures. If you look at the sec jet the air bleed is small brass tube that extends down into the jet. it has holes in the side of it. you can use a small drift and drive them down and out the bottom of carb top. very simple chore.

Oh thanks! The Tq is one of my favorites to mess with but I have not gotten paste the 12's with it. So hence, no real mods needed.

Any updates Diplomat360?

Nah, nothing yet, last week was our family vacation time, spent on the WestCoast (ahh, those guys have it made there, sun all year long...LOL), but I'm hoping to try out the larger secondary jets later on in the week, probably going to drill up to .156" as the biggest one I have is 0.149".

I will play around with the bigger secondary jet first, try to make that work with my current primary jet and the rods...my goal is to go for more air-flow (biggest secondary air-door openning) while staying in the high 12s AFR.

Hopefully I can report back before the weekend...stay tuned!

Alright...small update to report.

Couple of things actaully, I moved to a much richer primary jet, from 100 to 104, my thinking being this should feed the idle circuit a little extra fuel, while allowing me to retain the 2144 rods which so far have been a pretty good combination. I also moved to a 156 secondary jet.

Well...I'm thinking you can guess the result...the overall primary cruise/power is far too rich now...LOL...we are talking 12.2-12.5, and I've seen it actually dip into the 11s regularly as I near the 2ndaries openning. The off-idle shows that the engine is loading up with fuel. So this is far too much fuel...although strangely, once moving along (city cruise, so about 2K RPM) the motor sounds "better"??? I mean it is smoother, not sure how else to describe it...

The WOT on the other hand is pretty decent around 12.6, but I did open up the air-valve to the max .900".

So in summary, comparing this to my previous primary jet = 100, secondary jet = 143, rod=2144 I am looking at the following changes (the below numbers are just math jet/rod/area calculations, a direct comparison of +/- change):

IDLE % = 15.6
CRUISE % = 13.0
POWER % = 10.9
SEC POWER% = 19.0
TOTAL POWER% = 16.8

My next run will be to go back to primary jet = 100 and just look at the difference the bigger 156 secondary jet has.

440 with XE268 cam, Holley SD single plane intk, 727 with 3.23... Running an early Tq 6518S with normal idle screws (orig had holes in them) and with orig 2124 top. IFR drilled to 0.038" and then a 0.010" wire in the IFR. Idle mixture screws 2 turns out. Initial 22 degs with 11 degrees in distributor all in by 3,100 rpm. 18 degree vacuum advance can about 3 turns out.
0.098" primaries with 2024 rods about 3 turns from bottom. 0.143" secondaries. Oh, using inlet needles that will pass a 7/64" drill bit. Air door about 0.7", 1.5 turns. 0.028" pump shot on the slowest setting. Getting about 14 mpg on Shell V-pwr.

Sorry chargerjoert but what is IFR?

Idle Feed Restrictors

OK, many terms out there, please point out the passage you are talking about in the below circuit diagram:



Is it the:

1) RESTRICTOR
2) IDLE WELL TUBE
3) IDLE AIR BLEED
4) IDLE RESTRICTOR

LOL...yeah, many different points to adjust...which is what I feel makes it such a remarkable carburetor.

The IDLE WELL TUBE is 0.039" in my 9810S carb.

I have modified the IDLE AIR BLEED to accept brass plugs so that I can control the amount of air bleed, that was done mostly due to the lower idle vac signal, however playing with the settings ultimately led me back to the stock size.

I also removed the plug that leads to the RESTRICTOR, but I did not actually adjust the size of that passage.

yes, what I called the IFR for Idle Freed Restriction is the opening to the Idle Well Tube. Which you have reported is at 0.039".

Most, if not all TQ's I have, seem to have a 0.034" IFR stock. At 0.039" I'm guessing your's has been opened up. I'm surprised that with 0.039" opening the idle mixture screws are 4 turns out. However, your IAB changes will effect this. I have never messed with the IAB's. I open the IFR to get the mixture screws 2 turns out. If I over shoot it, then I add a wire.

Cruising is mostly on the IFR, so this circuit is all about the fuel economy. In your case, you may want to try reducing IAB size and see if that results in the idle mixture screws being 2 turns out. Spark plugs should be white if just light throttle cruising, but don't be so lean that coolant temp goes up.

Since my last post, I have had to limit vacuum advance to 16 degrees. And switched to 1950 rods.

Love the tech, thanks so much for this tutorial. This is huge for me. Thanks!