Trouble with a new Thermoquad Installation

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RFRisley

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I have a '67 Dart with a 340 (and drivetrain) from a '72 Duster. It had a Holley 670 on it which had a horrible dead spot when I nailed the accelerator. I played with the float and so on but it never really helped too much.

So I got a rebuilt Thermoquad off eBay and installed it as well as a correct choke. The Thermoquad runs very well when it is warm and has no dead spots at all. But it is a bear to start and runs like crap until it is warmed up, then it runs like a champ.

I adjusted the choke linkage so that the choke butterfly is closed when it is cold and all the way open when it is warm. But the minute I try to start it the choke butterfly opens up a bit and it will not start. I have to close the choke butterfly all the way and clamp it shut with a small vice grip pliers. After a few turns it starts for a few seconds and then stalls. I then remove the vice grip pliers and it starts after a few cranks. I have to keep it running by working the accelerator or it will stall. If I set the idle to keep it running when cold then it will race like crazy when warm so I have opted for the warm idle setting.

The Holley started up well and did not have any idle issues ... just the dead spot. No problems if the acceleration was gradual rather than nailing it.

I did bend the linkage that goes between the front and back choke butterflies so it does not open up much at all, but the small gap which is maybe 1/8" is still not enough to get it to run so I still have to use the vice grip pliers.

I was wondering if anyone had any thoughts. Thanks in advance for any input you may provide.
 
Hmm... sounds like you might have a vacuum leak. Try spraying WD-40 or similar around the carb base and notice if the engine speed changes.

You also might have to do a little tuning to get it to run just right on your 340. ThermoQuads are very sensitive to incorrect tuning and have to be totally calibrated to your exact engine setup. BTW what's that 340 got in it?
 
Assuming no vacuum leak, it sounds like you need to adjust the choke pull off. Look up how much it should open from a "72" 340 carb and bend the linkage to get that gap between the choke tower and the choke. If that does not get it, you can start closing it up from there till you get it where you want. I use drill bits to measure the opening. This is trial and error so keep after it. You should be able to get it almost as good as EFI.
 
I ran a thermoquad for years first on my 273, and then on my 340, and it was a bugger to start for a long time. We tuned and tuned and played around with it for a long time, and nothing seemed to work. What we finally discovered was that the resin center piece had warped just enough that gas was leaking back into the engine when the car was parked causing the car to flood. Took off the TQ and went with a Carter 625 and have never had an issue with start up since. Those resin centers are known for warping so just make sure it is in good shape.
 
Sounds to me like the choke is not adjusted right.
 
Thermoquad choke setup can be a PITA. Good luck!

I prefer a manual choke carb truthfully.
 
When you start it, put you hand gently over the choke horn. Your had will be acting as a choke. If it revs up/smooths out/ keeps running you either have a vacuum leak ( which can clear up when hot) or the choke needs to be adjusted. How much tension is on the choke plate when cold. You should be able to feel some spring tension when you push on it with your finger.

Garth
 
Sounds like the Holley needs a bigger squirter/pump cam or maybe a stiffer secondary spring.
 
I don't think it's necessarily a choke issue as my 318 started cold without much fuss even with the choke REMOVED from my ThermoQuad; granted it was at least 60* outside whenever I had to do that, but still...
 
Thanks for all the helpful info. I will follow the advice in a stepwise manner and see if things approve. I torqued the carb down pretty tightly and all openings either have hoses attached or vacum caps so I hope there is not a vacum problem, but I will check that out as well. Getting specs on adjusting a choke pull off might be a challenge, documentation on thermoquads is pretty scarce. Thanks again for the tips.
 
..............Adjusting the choke on a TQ is a very trying situation...........good luck..........kim........can u post some pics.........
 
check the squirters it dont take much to kinda plug em maybe but probally not
 
So I got a rebuilt Thermoquad off eBay and installed it as well as a correct choke. The Thermoquad runs very well when it is warm and has no dead spots at all. But it is a bear to start and runs like crap until it is warmed up, then it runs like a champ.
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Yep, nothing new there. Perhaps the pumpshot needs to be a bit more on time rather than a slight delay. The chke setting may need to be enrichened. This may have to be done via bending a rod. The settings on the TQ must be followed exactly. Otherwise, the carb is a little bratty.

I have the same issue on my 400. One of these days I'll get around to a minor rod bend.
I turn the key, she spins, then just as it's starts to speed up and kind of catch, I floor it and BANG right up.

Once the 400 is all warmed up (And it takes a big block awhile to do) it's an excellent carb, but not until warm.
 
LXguy said:
Sounds like the Holley needs a bigger squirter/pump cam or maybe a stiffer secondary spring.
Click to expand...

I agree...too bad you bought the "plastic" carb before figuring out the problem with the Holley it could be something very simple and the Holley is a much less pain to tune and run correctly..
 
I agree with stroked. The Holley was a pump shot delivery issue, easy to solve. Oh well, live and learn. Ethier way, have fun with it. Otherwise, your doin something wrong. ;)
 
Thanks for all of the suggestions. I adjusted the pumpshot, put in a new power valve, put in a couple of new size jets, etc. on the Holley and it did not solve the problem. I did however get the thermoquad to work properly. Here's how.

After fooling around with many thicknesses of carb spacers and gaskets I settled on 2 of the standard Mr. Gasket gaskets combined with 2 of the Thermoquad gaskets that you can get on ebay which are about 3/8" thick. They work very well with either the electric chokes you can get for a Thermoquad of the standard thermostatic chokes. The carb now starts when cold and after a couple of minutes to warm up it drives very well.

I did have to loosen up the fast idle control lever which was tightened way to much so it did not move. I also had to bend the fast idle connector rod a little to shorten it about 1/4". This allowed the fast idle control lever to move so that the fast idle speed screw was engaged when the engine was cold and the curb idle speed screw would be engaged when the engine was warm.

I also bent the choke connector rod which adjusts the position of the choke valve so that it is closed when the engine is closed and open when the engine is warm. The choke connector rod was too long on the carb I got from ebay and I modeled the length after a Thermoquad my son got from a friend that was formerly on a Barracuda with a 383. The length I set was 2 3/16" center to center of the rod ends.

Once I got a service manual with information on a Thermoquad in it the process was easier as the jargon was explained, but there was a lot of trial and error. I got one from rockauto.com for a 1973 Challenger.
 
NICE! Someone who took the time to learn the carb. SWEET!

You got a service manula and/or carb from rockauto.com?
 
Glad you figured it out. I also appreciate that you put forth the effort to make the Thermo-quad perform correctly. THE most common problem with a Themo-qaud is the guy working on it (which all too many times has been me). Once you learn how to make them perform you will love them. For a street motor I prefer them over Holleys.
 
grimreaper said:
Glad you figured it out. I also appreciate that you put forth the effort to make the Thermo-quad perform correctly. THE most common problem with a Themo-qaud is the guy working on it (which all too many times has been me). Once you learn how to make them perform you will love them. For a street motor I prefer them over Holleys.
Click to expand...

Very tue. While there not easy like a Holley to set up when there all out of wack, ya know there, well, a bit finicky to work on and get used to, once set up and correctly tweaked, there really a surprising carb and quite livable in many applications. I had a few fits when I first got one. The wrench turner was himself a loose nut. (ME!) and once I got it where it was supposed to be. I was quite happy with it.

There very solid. Jet it, set it, forget it carb. Just keep the heat away from them and give it time to warm up right. They won't letcha down and fall out of tune and get stupid on ya.

I love running them and then opening the hood to the looser of the race. Watching his face ethier drop or get confused with comments like;

"WTF is THAT!!!!!????" / "Who makes that?" Or "Is that a stock carb?"

Ans... It's an alien device designed on the outter rim of the galaxy. It was a gift in trade for a few cows."

Right now I'm running a 9800 TQ w/electric choke/GM replacement model on my 400 Magnum.

:toothy10::toothy10::toothy10:
 
Rumblefish....

Does your Thermoquad try to suck your hood in like mine does???:burnout:
 
Good intel in this thread! I have a T-Quad on my '74 Voyager (factory 360 4bbl) and am having problems with it (won't start, rough idle when cold....sometime when hot as well). I have a Holley Reman T-Quad still in the box to install if I can't get the original to work right.
 
yellowdartdave said:
Rumblefish....

Does your Thermoquad try to suck your hood in like mine does???:burnout:
Click to expand...

LOL! No, the intake below it doesn't restrict it. At least that I have noticed, but the seagull it eat up might disagree...... :toothy10:


Ontos Get those instructions and set it up!
 
I've been running a Thermoquad on my Demon for 20 years. Years ago a buddy of mine bought a strip kit when you could still get them. I found a setup that works even without a choke.
 
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