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Thermoquad questions

Sonny

It’s all fun til the rabbit gets the gun.
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Tuning my new 440/thermoquad 850 and have a few questions:
1. My air/fuel ratio at idle is about 16 and the adjustment screws out about 4 full turns out. Sound right?
2. I blocked off the heat risers. Does that mean I can’t use the choke thermostat on the stock intake? If I can, what is the wire for and where do I get power from (or is it ground)?
3. When I flick the throttle the end of the rpms (about 1000 rpm down to norm) take a while to come back down. Thoughts?
 
1. I have to let a carb expert answer that one for you. Sounds rich. I always forget which way is which with the bleed screws. I thought IN was lean but maybe not. If it won't lean out you'll have to see if it's not on the idle circuit of the carb.
2. If there are wires involved you don't have divorced choke. A wire would indicate an electric choke. Wire would more than likely be positive. Just find a key ON poster source. They typically ground themselves unless you see a negative terminal. Only the divorce choke would be an issue if blocked and even that will still work, just slower.
3. See problem one more than likely.

Is the choke fully open?
 
1. Sounds a touch rich. But I am not sure how your getting this number.

2. Use the stock choke even with the block off. The wire is for a heated thermostat. It connects to a little resistor block. That is fed by the blue wire (12V key on) off the ballast resistor. I added a pic of the resistor.

3. A little stronger spring?

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16:1 is about typical for smogger TQ calibration. The TQ is about the only carb that can get away with idling that lean. If it is not behaving well due to a lean condition,Aside from doing making permanent modifications, you can tinker around with float level and metering rod/ jet combo's. You never said how it was behaving? There is also the air bypass holes in the front of the choke horn. Plugging them will richen you back up big time, in my experience.
 
16:1 is about typical for smogger TQ calibration. The TQ is about the only carb that can get away with idling that lean. If it is not behaving well due to a lean condition,Aside from doing making permanent modifications, you can tinker around with float level and metering rod/ jet combo's. You never said how it was behaving? There is also the air bypass holes in the front of the choke horn. Plugging them will richen you back up big time, in my experience.
Thanks. It’s runing pretty good. Takes a bit of feathering the throttle when cold. I’ve read that 14 is a good a/f typically but if 16 is the norm for that TQ then that’s the info I was looking for.
 
Idling is OK. You don't want to be 16:1 under any kind of load.
 
Idling is OK. You don't want to be 16:1 under any kind of load.
Under acceleration it drops to 10-14 depending on my foot.
 
1. I have to let a carb expert answer that one for you. Sounds rich. I always forget which way is which with the bleed screws. I thought IN was lean but maybe not. If it won't lean out you'll have to see if it's not on the idle circuit of the carb.
2. If there are wires involved you don't have divorced choke. A wire would indicate an electric choke. Wire would more than likely be positive. Just find a key ON poster source. They typically ground themselves unless you see a negative terminal. Only the divorce choke would be an issue if blocked and even that will still work, just slower.
3. See problem one more than likely.

Is the choke fully open?
Yes I wired the choke fully open for now.
 
I still don’t hear/feel the secondaries coming on. Would I?
 
Yes I wired the choke fully open for now.
I had my numbers backwards, 16 is lean not rich. Choke wouldn't be closed in your case.

I always wondered if the secondaries open too. I have a brand X with a Thermoquad and you know when that thing opens up, BAAAHHH WAAAAHHHH. I never ever got that sound out of a Carter AVS or AFB.
 
4 seems a bit much for your idle mixture, but it does vary depending on engine configuration. I am currently running 2 1/2 turns out, but I tune by starting at 1 1/2 turns out, and adjust accordingly for best vacuum and idle smoothness, then ad up to 1/2 turn out. So if you turn in until idle starts getting rough, then back out 1 to 1/2 turn should get you into that ball park.

Easy way to check secondary's is to hit wide open throttle while watching the carb when in neutral or park, you will see the air door open when full throttle, and as 69L48Z27 said, it is obvious sound when they open, but check to make sure that both secondary and primary throttle valves are opening as well.

Regarding the secondary adjustment, make sure that your linkage from primary to secondary is set so that both primary and secondary throttle valves are maxed out at same time with wide open throttle. Second, make sure you have air door adjusted properly, typically it should be 1 1/2 turns on the spring once it makes contact with the stop, if you are two rich, you can adjust in increments of 1/4 to 1/2 to get it dialed in, this adds tension to the spring, and you can easily break it if you go beyond 3 turns.

One other thing to keep in mind, my thermoquad didn't really perform well and was difficult to tune when running 10% ethanol gasoline, when I switched to ethanol free, the performance was so much better I couldn't believe it.
 
Hey idrive, What is the list number on your TQ? Also Sonny, don't expect the secondaries to be completely vertical. They should stop just shy of 90 degrees. idrive You are right on the money about the ethanol. I just converted a TQ to E85 for a customer, They use 3 air bleeds in the idle circuit. I had to eliminate 1 completely, and cut the other in half, and open all the feed holes up significantly to get a good quality idle mixture. It was a smogger 9103 list.
 
Any reason that you are running an old T-Quad ? There are much more tunable carbs available today. Mopar used the AVS back in the early 70's. T-Quads later for emissions. Great carb in its day, but limited in parts and tech info today. The T-Quad carb number for your app I believe was the #4738 . 440, non egr, a/t non-Calif.
 
Any reason that you are running an old T-Quad ? There are much more tunable carbs available today. Mopar used the AVS back in the early 70's. T-Quads later for emissions. Great carb in its day, but limited in parts and tech info today. The T-Quad carb number for your app I believe was the #4738 . 440, non egr, a/t non-Calif.
I respectfully disagree sir. I don't think there ever was or has been a more tunable or versatile carb for the street. When you get one setup right, they are the next best thing to injection. 4738 was never a TQ number.
 
Any reason that you are running an old T-Quad ? There are much more tunable carbs available today. Mopar used the AVS back in the early 70's. T-Quads later for emissions. Great carb in its day, but limited in parts and tech info today. The T-Quad carb number for your app I believe was the #4738 . 440, non egr, a/t non-Calif.
The TQ was first developed as a racing carburetor and adapted for street useage later. There is almost no reason to discard this carb in favor of a square bore carb in most applications. The problem with TQ’s is lack of tuning parts, full understanding and tune ability with most people because of the lack of jets and rods. The spreadbore design is a plus and minus. The squarebore is normally an equal 4 way distribution of air and fuel while the TQ has the small and large sides. This also makes single plane intakes for the speeadbore more difficult to have a good fuel distribution which is not ideal in squarebore intakes ether even after pro porting.

I still contend the TQ as an excellent street & street strip carb.
Once you learn this carb you will be very happy with it.
Like all Carter carbs, the rod and jet combos are difficult to get the hang off. It truly sucks taking the top of the carb off to change jets. Adding in the complexity of the rods multiple diameters and how much or little a rod can do for a tune.
Tuning my new 440/thermoquad 850 and have a few questions:
1. My air/fuel ratio at idle is about 16 and the adjustment screws out about 4 full turns out. Sound right?
2. I blocked off the heat risers. Does that mean I can’t use the choke thermostat on the stock intake? If I can, what is the wire for and where do I get power from (or is it ground)?
3. When I flick the throttle the end of the rpms (about 1000 rpm down to norm) take a while to come back down. Thoughts?
What is the TQ carbs number. This can be a huge issue. Earlier the carb is the better unless it is the first year of the TQ. It meters the air and fuel differently.

1: I’m betting you have a a/f gauge since you stated a a/f number so, to go on from there, correct the idle a/f ratio first and as said above, the idle screws should not need more than a total of 3 turns out, which is a lot and still pointing towards the jetting being lean. Which maybe a necessary (or the reverse being rich) evil due to lack of rods and jets available to you at this moment.

2: Blocking of the heat to the intake basically renders the heat riser & choke useless. The electric wire is an emissions part designed to speed up the heating of the choke element to reduce emissions as per the Fed’s. Pictures above is the part you can use to help the choke to operate. How well it operates is a mystery to me.

3: The throttle flicking is the engine/carb out of balance trying to find where it should be. I believe it is a condition of to rich and/or the engines vacuum ripping fuel out keeping the rpm’s up when the throttle is closed. I’m not totally sure. This is a occasional problem for me. Tune the carb and it will come back the way it should. In tuning the carb, make sure you also tune the distributor. When I keep messing around with it, it normally goes away.
 
My mistake, the #4738 was the AVS part number. I know he history of the T-Quad and agree Properly tuned is an excellent carb. Point was that few are currently in the know on setting one up. And as I said, limited parts and hands on knowledge in the tune. I ran one for many years on my 340 Challenger. Just saying that tune up info is more readily available for other carbs, like the Edelbrock AVS replacement. Not everybody has the same skill set. Some are good at fuel systems and some are not as good. I just like to keep it simple. Just wondered why he chose a T-Quad. Not every ones first choice unless it came with the engine/intake, some one gave it to them or they read some articles on it. Didn't say it was bad. Just not the typical persons first choice. No body ever asks why someone has some particular component. Sometimes it just came that way. We sometimes seem to just jump in with all kinds of advice with out a back story. JMI.
 
Hey idrive, What is the list number on your TQ? Also Sonny, don't expect the secondaries to be completely vertical. They should stop just shy of 90 degrees. idrive You are right on the money about the ethanol. I just converted a TQ to E85 for a customer, They use 3 air bleeds in the idle circuit. I had to eliminate 1 completely, and cut the other in half, and open all the feed holes up significantly to get a good quality idle mixture. It was a smogger 9103 list.
So, originally my 340 used the 6319 small bore thermoquad, but as I restored my car and tried it with boosted compression and bigger cam it was too lean. I went next to 6322 which was the large bore TQ for 73 and I have a couple of them and tried, and they were close, but I couldn't find one that was in good working order, meaning one that mainly had throttle rods that were still in good shape and not worn so as not to have any vacuum issues. I found last year a real good 9023s which is from 74, and it is almost identical to the 6322 except it has bigger secondary rods, and i rebuilt it with new floats, and all the internals, new leather accelerator pump, and now that I have it dialed in, it gets up and boogies, idles great, and wide open throttle is almost perfect with no bog, she down shifts goes wide open and hauls ***, and when I power brake, she squats and spins the tires and goes a bit sideways!

My reason for thermoquad was really at first to keep stock look, if you have seen my car, you will know.
 
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As you have so eloquently shown, it is a process to get it right. These parts were designed, tested and calibrated for very specific applications eg C.I., cam spec, rpm usage, CR , fuel etc... Hence.. so many part numbers. Once you change something in the factory package, adjustments will have to be made to regain that performance. Not all are up to the task or have the patience.
 
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A lot of good info above. Thanks for the detailed responses. Why did I chose the TQ? It came with the 1978 440 I bought and I wanted the extra fuel boiling/vapor lock protection. I do have a larger cam, .030 over bore, and raised Keith Black pistons. Same 452 heads and stock intake. Using an Inovate air/fuel ratio gauge. I can go to 5 or 6 half turns, but a/f goes to 19. Isn’t that too lean? Attached are some TQ pics after rebuild.
 
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View attachment 695509 View attachment 695510 View attachment 695511 View attachment 695512 View attachment 695513 View attachment 695514 A lot of good info above. Thanks for the detailed responses. Why did I chose the TQ? It came with the 1978 440 I bought and I wanted the extra fuel boiling/vapor lock protection. I do have a larger cam, .030 over bore, and raised Keith Black pistons. Same 452 heads and stock intake. Using an Inovate air/fuel ratio gauge. I can go to 5 or 6 half turns, but a/f goes to 19. Isn’t that too lean? Attached are some TQ pics after rebuild.
Here are the numbers on top and back of throttle side:
 
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