1971 'Cuda 340 Dyno Test - Thermoquad Opens Up 

the thermo-quad was the first carb that I tried to rebuild on a 383, I was still working on it at 1am, when my Pop came to help me, I went to bed at 2am, got up at 5,30 am my car was gone, Pop took it out for a test and it ran like a champ, thanks for the flash back Dr. Nick, cheers.

When I was a teen, I apprenticed at the county shop as a maintenance mechanic, we had a few old Sattelite interceptors with the 400 lowdeck and of course an 850 thermoquad, at that time I knew nothing about them and had only worked on AFB and BBD 2 barrels from mopar because my friends always asked me to tune or rebuild them. The first time I saw the thermoquad, I was instantly hooked because there really is no other carb that looks like it! I never saw something so exotic in a factory car and I had to wonder if it was at least part of the reason why the interceptors ran so strong. My mentor who knew everything about all the vehicles in the shop told me that it is the most advanced carb in the shop because of the materials and the way Carter chose to design them made them far superior to all metal carbs. The phenolic resin (floatbowls/ body) was the true genius because it keeps the fuel cold and therefore makes for a denser charge allowing leaner needle and seats and less fuel consumption we were getting 5 to 10 mpg increase swapping in thermoquads and power across the board. I learned a lot from my mentor the 2 years I worked there, and it was so much fun learning about big block power because I only worked on small blocks for my friends but got big block power out of them through tuning and sometimes cam and other upgrades

I love thermoquads! Spent lot of time modding them. Out performed Holley street carbs. For starters. Make sure to adjust accelerator pump travel to maximum. No slack! The the air valve, loosen till drops (make sure to keep screwdriver tension so dont unravel) and then turn back tension about 1.5 or so after valve closes. Better to have more tension than less. My GM friends have tried them on their Rochester equipped cars and and they flat out, outperformed them.

...the fact that the kid knows what the 'Fonzarelli Touch' is, and that he's hanging around in this shop...Nick should be grooming him as his successor for when he retires.......and that his name is Nico is an added bonus! Nic's Garage

I have 11 thermoquads. Nothing sounds better than thos 2-1/4 secondaries opening up

Says a lot about Nick that he not only admitted his mistake and showed the correct way, but gave full credit to the carb guy for a perfect job. You can believe him, that's why people like him so much, it's honest

We all learn things over time, as far as I'm concerned you are the best mopar guy in the industry, if I ever get rich enough I'll have you build a few of my dream builds like the 1000hp 400 lowdeck with 426 hemi crank with long rods and special raised pin pistons from Keith black. Another one is a 360 with 340 forged crank, forged rods and high domestic pistons that runs 8000 ram all day and produces 700 hp basically an early 70s Nascar engine. AFR heads, custom roller cam, timing belt instead of a chain, electric water pump and a custom sheet metal intake that I build with a holley 800 cfm carb

I know you don't like headers Nick, but it's good for another 15+ h.p. boost and a lot more on the big blocks as you've shown. For this 340 to me, it'd be worth it. Except for factory original cars that people want to keep that way, almost every 340 I've seen and worked on over the past 30+ years, they've almost all had headers on them. Believe me, I love factory original cars, but if it helps to get some more power and can be changed back to original without damaging anything, I usually get them. Then again, I'm the type of guy that shoehorned a 440 with the 727 attached, and put headers into my 72 Barracuda all by myself in the driveway! Like you,if it has to be done,if even by myself alone, I used to get it done!!! That was in the 80s many cars, trucks and moons ago. Thanks again Nick and company. Great to see the younger generation learning about engines with you too!!! He can have no better teacher!!!😁👍

Good looking nephew Nick, I see apprentis in his eyes, I thought thermoquads were in Chevys, all of my Mopars had Carters, then again I didn`t own one after 1970, My buddy had a 71 Cuda 340 auto, I didn`t know the stock HP, the Cudas were great with 340 or 383 they weren`t too nose heavy, I think 340 `s handled the best, it sounds great Nick.

I was sitting here yelling "stuck float!"

71 340 cuda, I have one sitting in my garage. 😁

Nico seems like a pretty chill guy. Keeps a sharp eye on his boss. 🙂

Someone gave me a '67 Charger back in 1992 (still have it, in fact), and I got tired of rebuilding the leaky old 2bbl on the 318, so I picked up an Edelbrock Performer, and a funky looking plastic carb from the wrecking yard. It was a completely different car with the TQ, but it wasn't until some punk in a Jetta tried to get around me on a freeway on ramp that I realized that my dual throttle return springs were so strong that I'd been driving for two weeks on the primaries. I mashed the throttle and the whole car seem to vibrate, and I backed off before realizing that it was actually the howl from the secondaries. I floored it and dropped the Jetta. I had so much fun with that car before the 318 died that it'll be hitting the road again soon after 20 years in the garage with a warmed over 360 - and the very same Thermoquad I put on in '92.

After getting a truck to run AND drive these last 2 days, after 5 years of being totally parked, I'm in the right place to relax. Sing the song of my people, you sweet little 340. You are my all-time favorite engine....EVER.

Nick I love your dyno videos and testing a 340 which has always been my favorite engine. I did my apprenticeship in the 1970s and specialized in tune-up electrical and diagnostics. The number of thermoquads I have overhauled and tuned would probably in thousands. As to your lean condition the metering rods came from the factory set to low. There is a screw adjustment on the power piston under the red clip that you can adjust to clockwise to raise the metering rods to richen the mixture . do this at 2100 rpm. As you raise it the engine rpm will increase. I always set it to 1 1/2 % co at 2100 as my Allen Smart Scope had a 3 gas analyzer but did not give A/F ratio. The other problem you have is that your air door spring is set to loose. You will probably have to tighten by about 1/2 turn. Also on the street the accelerator pump needs to be adjusted to give about 1/32 inch more stroke than what the spec is. One other thing you can do is install a quick curve kit in the distributor, the factory curve is way to slow. Unfortunetly Mopar no longer sells this kit but a Mr Gasket kit might work. As for the not returning to idle check that the secondary plates are closeing completely when you go back to idle.

Always liked the way thermo quads work and sound.

My first experience with a thermoquad came in the way of a 72 340 Duster 3 speed on the floor with 3:92 rear gears. It belonged to my younger brother. I also owned a 72 Duster. Mine too had a 3 speed on the floor and rear gears of 3:23. But mine was a 318 that we added headers, 4 bbl. Edelbrock intake with a 750 Carter avs off a 383. Also cam dynamics cam and recurved distributor. That thermoquad carb when set up right was killer. It stayed in tune and delivered great performance results. We played with the rear air flap until we had it perfected. When that 4bbl came in with first gear the tires would light up at any speed in first. In second it would break traction for just a second or two. We never had to set it after the adjustments were made. I own a 340 today. And I still have a stock cast iron intake with a thermoquad carb ready to drop in when I get tired of the avs that’s on it now. But I also like the 750 avs. Great reliable carb in its own right. Great video Nick. Long live the 340.

Finally, we have some true horsepower numbers on these legendary motors. Lot of B.S. out there.

In Baltimore,my friends Dad had his parking place in front of his spot occupied by someone . He ran a hose up from the cellar and hosed the car down for several hours out his front window. The interloper came back in the morning . The his car was frozen under 6" of Ice!! It took the interloper 2 days to chip it out!! Never saw him again.. 😂😂😂😂😂

Hi Nick & Crew: Love the show, it is unique on RU-vid. This 340 build reminds me of my wife's (may God rest her soul) '74, 318 Gold Duster. It had the same/similar two stage carb. We live in Nashville,TN, and in winter mornings were 15F warming to 40F around 3pm. Anyway, I drove it and learned how sensitive and lean running it was. Never had a carbon encrusted spark plug @ replacement intervals. The 340, right at the start you took the primary choke butterfly valves off-line. I believe they serve a dual purpose. They close completely on cold starts, but they close partially at idle. I noticed this with my instruction to this carburetor on cold nights leaving work. It was at the cusp of normal Temps but not quite. If I so much as removed the air filter cover momentarily, the choke should flip open (that partial I mentioned) and I'd be screwed. Needing to work the throttle until warm enough to idle. I think your rebound problem is connected to the primary choke being held open, causing a lean mixture.

Well I've been driving and racing 1971 340 engines since 1971. That is not a 71 Thermoquad. Probably a 72. The 71 carb has idle screws at an angle. Also the choke linkage is on the end of the choke butterfly outside of the airhorn. Plus the 71 doesn't have the screw adjustable piston on the metering rods. The accelerator pump should have more available stroke. I can send you a picture of a 71 carb. The exhaust manifold on the left side (passenger) is a 70 or earlier, too. Hate to nitpick but not original stuff. Yes I'm 71 years old and happy to help.

Back in the late 70's i picked up a Charger 440 RT with 45K miles on 'er for 2 Hondo'$, top over hauled the Thermoquad (first time ever) fired right up rant clean, drove off into the sunset! :) They are somewhat more complex than Holly'e or even Quadrajet and just as fickle at times! GodSpeed Nick! Carry on!

The most difficult part of setting up the thermoquad is the settings for the choke and pull off as it involves multiple steps starting with the distance from the bottom of the throttle plate to the hole in the choke rod lever. If not correct all the other adjustments are out. This is important as the pull off also affects the secondary air door opening. If you tap the air door with your finger it should close all the way every time with just a little bit of a snap. I have the special carter tool for the lock ring that is hollow to allow a screwdriver inside of it to turn the spring adjustment, but you can also do it with a large screw driver for the lock ring and a smaller one for the spring adjustment. Properly adjusted the TQ gives you the best of both worlds, exceptional fuel economy for everday driving and cruising with instant throttle responce when you floor it and great horsepower. You have to love it when those 2 1/4 inch secondaries open up and the great roar that came from them. 1972 340 Rallye I had back then also had the air cleaner with trap door at the back that would open at the same time and add to the roar of the air rush. I could pull away from any Camaro and leave them behind and still get 25 miles per gallon 75 mph. With just a few tweaking adjustments this 800 cfm carb performed flawlessly on all engines from 318 to 400 cid. The 440 got the 850 cfm version. Just as a note the 71 TQ was known as the solid fuel version and was used just the one year. It was redisigned for the 1972 and up and was even a bit better than the first version. Looking forward to the next 340 dyno session you have comeing up.

Hey nick I thought you might find this funny, I was watching the car starz video guy, and just for the hell of I checked the challenger one from vanishing point, apparently some of the cars werent originally white, they were actually green like your actual car, it shows up in one of the scenes in the desert as theirs a quarter panel dent, and you can see the green underneath it and it looks to be the same shade of green you found your 440 in so your vanishing point clone is actually more accurate than you realize and you dont need to feel bad about respraying it as it is now just even MORE movie accurate lol

The 71 factory 340 intake was the best one. Last 3 numbers 100.

I was a carburetor mechanic back in the seventies. When this issue would happen, we would rev the engine to 3500 RPM and then shut the choke for a second or two and then let the engine catch up to clear out the excess fuel. Sometimes their are particles in the metering system and this would purge them out. Hope this helps.

Great to young guys learning the basics, air , fuel , spark

Never met a T-Quad that I liked. Back in the day I'd install the Mopar throttle lever on a GM Q-jet and toss the T-Quad over the fence. The neighbor would promptly toss it back because he didn't want it either.

This was a fun flashback. I inherited the 340 gene from my dad, and, for a too-short time, in the early 90s, I owned a 71 Demon 340. It was the first, and so-far only, time I did a cam swap and top end work. I tell you, I was more nervous firing that up for the first time for the break in than I was at my wedding! Luckily, it went smoother for me than for Nick here!

I had a 72 Duster 340 with the 7.62 Thermoquad. It was like flushing a toilet when that thing opened up! Loved that car

I'm commenting before watching the video! I had a '71 340 Demon w/Torqueflite. The 68-71 340's were jewels!! Mine spun a main bearing at 105K and after giving it to a clown to rebuild, it never ran the same, so I sold it. Rated at a ridiculously low 275 horses, they were actually putting out about 320-325!! I expect Nick's know-how will add 10-15 hp to that! The man is a magician on Mopars!!! Now i'll enjoy the video!!!

Nick you are a Master at your craft. Shows what hard work and some smarts can do.

From decades-old, possible flawed memory, the distributor vacuum advance nipple was always connected to the "ported source" (shown plugged here) nipple on the left front of the carburetor whereas the nipple at the rear of the carb, that it is connected to here, is manifold vacuum. Don't recall ever seeing that on these early non-emission control TQ carb engines. A minor linkage adjustment likely is hanging the secondary throttle plates open very slightly after a wide-open excursion of the main throttle rod. The relation of the primary choke rod is very critical to that whole operation, as the secondary throttle plates are blocked closed when the choke is on any little bit, and that can work to the opposite when not adjusted correctly. We battled and solved many-a Thermoquad issue right out of the factory back in the day thru good old trial and error. God, I'm old... Efaristo, kai na eisai panta kala! PS: Wanna talk about needle seats for the floats backing out in the cover, and other anomalies? Let me know... lol

If it was me, I would check the bolts that holds the carburetor together the bottom plate in the top part of the carburetor. See if they need snug down some more remember you got 2/2 there that have the potential of leaking vacuum. This is six in a row Jim from Kennerdell Pennsylvania

I was taught by an old timer years ago a few tricks with spread bore carbs including the one with the rag (or your hand). One was that if you flooded it was to prop open the secondaries with a screw driver and crank it to clear it. Sure worked on the Q-jet. I love the spread bore carbs.. It was cool to feel the hard spot in the throttle on a Q-jet right before the secondaries opened up and the trans down shifted!!

I had a 71 Road Runner 340 Air Grabber, with a Thermoquad , I loved that carb. The secondary air door needs to be set firm.

Now, besides all the experience and skill. Nick has The fonzarelli touch!!! I love to see nick and nico working together!

Nick is like an orchestra conductor - every note is perfect

"The Fonzareli touch". Wow Nico, that is a blast from the past! And not even your past by a long while. Indeed that is what the Fonz would do. Very apropos.

What a nice 340 ! The early thermoquads were excellent carbs. It pays to read the manual because once sorted, it will perform like fuel injection. Great job Nick, and I'm glad you're feeling, George.

Fun the scurry around a new engine....every time gross tuning, paint burnoff, and big time listening...

Be careful with all those paint fumes when breaking in those engines Nickos maybe run some extra ventilation or wear some kind of mask. Great job once again keep safe best regards from Down Under Australia

Liking the Thermoquad❤️❤️❤️

I alsobused the black phenolic 1" carb spacer on my 440 to help keep it real cool. The spacer i had was on one side molded for a spread bore. The other for standard 4 barrel. I highly suggest using that. You can learn to master the thermoquad if your patient. Its not difficult. I drilled all my jets 1 size bigger on drill bit. Did all the right adjustments and ran so crisp and flawless with no stumbles or lag ever! Also, there were 2 thermoquad styles, lean-burn(with lean burn vacum port) and non lean burn. Scarf these up for cheap at swap meets then use the best non warn parts from them to make one great one.

People are seening now how touchy a carb can be. Good work Nic Good work George

The mighty thermoquad . CHRYSLERS answer to the Quadrajet . I've worked on many of these carbs over many years. The plastic phenolic center bowl section can and was alot of trouble as these carbs aged on hot engines . Remember this carb was also used on the terrible Chrysler LEAN BURN engine control systems . The engine heat really was the enemy of the thermoquad and warped the center phenolic bowl assembly . Like them when they work , hate them when They don't. Id only run that carb if you absolutely had to have the car and engine completely original . Nick fighting tha5 darn carb brings back many memories of m6s3lf do8ng the exact same thing ... 😮 Scott in soca

2 other notes I want to pass on to you Nick, the choke linkage is designed to Stop the secondaries from opening when the engine is not fully warmed up, to me this is absolute genius on the designers part. Also that tiny screw in the middle of the airhorn between the primary and secondary ventures is the master mix screw for the primary rod height . So if you ever do have a lean or rich problem in the primary circuit you can easily adjust the AFR with this screw while the engine is running! Another genius idea from the Carter engineers that I find works as good as fuel injection or shall I say is as reliable. I look forward to more shows with thermostats involved because in the 70s into the 90s that was the go to carb for mopar fanatics like me who actually studied the thermostat and really all the great mopar carbs that were used on in my opinion the best engines Detroit had to offer at the time

Not surprised it's running lean at idle. My '72 340 with a TQ was very lean from the factory and had to richen it up to get it in the ballpark. Also I noticed the secondary air door seemed very loose earlier in the vid but didn't seem to be an issue when you did the pulls. Thermoquads run like a champ when they are dialed in.

Thermoquads are actually great carburetors I ran a lot of them back in the day. What their main problem was is the plastic middle section cracking a lot of time internally most the time causing vacuum leaks and all kinds of problems. But once you have a good one and have the jetting kit rods etc.. they were very good drag racing carbs. I routinely ran low 11s and high 10s with thermoquads.Offenhauser Port-O-Sonic intake with the epoxyed Popsicle sticks in LOL. with a built 340 in a Duster. Did some 440s to like that to with different Intake though. I ran them just to be different from everyone else. I have two of them NEW in the box still in the factory plastic in my garage bought them in 1978 one is the same carb you have in this video and the other is for a 400 big block for a Roadrunner I think a 73 400 engine. Anyway great video as always Nick and crew.

Nice little engne, I have said this to my nephew and others, the tuning is critical on any performance engine, or stock engine like this one. if only more DIY-ers and mechanics knew how to set up the automatic choke. For a manual setup, the choke pull-off eliminates jogging the choke.. and the engine will start up and run on the first or second compression stroke. If the engine doesn't start right up, the choke isn't set up correctly. One pump on the gas pedal, wait 2 seconds, crank and it will start and run by itself. The exhaust damper is essential for faster warmup, always a mistake to remove it. And fellas, a street engine prefers at least a 180 degree thermostat. The pistons round up, and your engine will last longer, no worn skirts, no blow-by. Your engine will love you, and serve you for the long run. Never run a street car without a thermostat, (or run hard when cold) fatal mistake. I do think this engine would benefit greatly by a stiffer cam, maybe .488 lift at the exhaust and 230 degrees duration, for the top end that these engines are capable of. The cam I suggest would have a slight chop at idle, good vacuum for power brakes.

Hi Nick I have played with these carbs since the mid 80s and have had the odd one with secondary butterflies with a sticky throttle shaft and don't close fully after full throttle, that was the problem when you had high idle after full throttle . I have just finished a 318 mild build with a Thermoquad and its running sweet , and with no choke it will start after 3 days without touching throttle, though it is summer in Sydney. I do love these carbs for street use, good cruise economy , power and sound when opened up.

When tuned correctly the thermobog was a decent performer . Great fuel mileage if driven correctly.

Great to see you back George! Healthy George and a healthy 340. What could be better!

Beautiful running, sounding and looking 340. That choke well was genius

Yeahhhhhhh the manifold paint went from silver to bronze!!!

Thermoquad was the best carb I ever had. Had a 60 over 360 that ran like a scalded dog...460 hp

A good functioning thermoquad is a great carb. Same goes for quadrajet carb. However- both are similiar in bad attitude when acting up. Makes you want to throw them in the scrap heap(dont do it- save until one calms down then go about FIXING it.) Thanks for great content. Health and Wellness for all.

I will add to my prior comments that the thermoquad was an emissions 4 barrel . Lean primary operation was built into the carb . I always ran into lean running on these carburetors and the rag on the carb covering the airhorn completely and engine is not choked off tells the tale . Scott in soca

I used to take the 318 that was original to my Dart to 5500 at the WOT shift point with the stage 2 shift kit in the 727 I swapped to. I had a 9800 aftermarket Thermo Quad, love them and I do have a strip kit and plenty of spare carbs and parts.

I have rebuilt a lot of thermoquads. I run them exclusively on my 72 Charger, it will not run without a choke even in Florida. Sounded like the needle and seat were sticking. They are finiky but they are the best street carb.

When I was a young guy without a clue about many things, I had a 71 'Cuda with the 340. The car came from the factory with the Shaker hood I loved the car but didn't really know what I had and I sold it. I've sold other cars thru my lifetime that I liked but the 71 'Cuda is the one I should have never sold.

Adjust the metering rod tree! Small flat blade screwdriver, turn clockwise to lift the metering rods up to richen the primaries!!

I've always liked the sound of the thermal quad carburetor back in the 80s diplomat police cars they sounded amazing.

WOW had to do a double take. Nico sure looks like the Fonz. I think he might be Nicks favorite Nephew because I've never seen him let anyone else touch his dyno.

Thermoquads - notorious for top cover warping and allowing air leaks.

I worked with thermoquads for many years.....theres several adjustments.....i see two thats fighting you here....the spring tention on the rear air vane isnt wound tight enough...changing the tention can fine tune the mixture......the second is the needles....a small screwdriver adjusts the hight of the needles....whoever rebuilt that carb didnt properly set the air valve tention and set the needles to the stock height....

Always enjoyable watching a master at his craft. Thank, you Nick.

I have watched several people that claim to be carb experts that don't seem to understand how a choke works. They jam a screwdriver in the carb to block the choke open then have to pump the gas pedal dozens of times to start the engine then keep pumping the gas toee it running. Most carbs have some sort of automatic choke. Mechanical or electric. Don't really matter which. Pump it to the floor once then release the throttle. This set the choke and high idle. Leave the throttle alone, crank engine till it starts. If everything is anywhere near close on the carb it should start right up and idle about 1500 to 1800 rmps. Let it idle this way for a minute or two then tap the throttle and it should drop down to regular idle speed with the choke mostly shurt to keep it running. At this point you should be able to drive the car. If you are trying to fully warm up the car, let it idle till the temp gage starts climbing near operating temp and the choke butterfly is fully open. Then do what ever tuning you feel it needs. When thee chokes get to acting up there are ways to adjust the amount the choke operates. You can adjust them to one quicker or slower, depending on ambient temps or to compensate for wear on the mechanism. Some of the early cars had a manual choke, this worked sort of the same way. Step on the gas to the floor and hold while you pull the choke knob out fully. Release the gas pedal. Now with your foot off the gas, start the engine. It should start right up and run on high idle. Once it starts, depending on ambient temp you may have to push the choke knob in to keep the engine running. It's kinda of a feel fof it thing. Quick and easy to learn with just a bit of practice. As the engine warms up you push the choke knob in. After a bit you will have the choke knob mostly in you can srat driving. after a few miles you can push the choke all the way in and be on your way. Often some auto chokes become problematic, for these they sell a kit to convert to manual choke.

It's far from a wreck This factory fresh rebuilt 340 belongs to Carole from Quebec and it's undergoing a thorough Nick's Garage check Nick and Niko have to break in the cam but a starvation of fuel wasn't part of their plan If anyone can fix it Nick's Garage can Thanks Nick Niko and George Big shout out from London

Best combo ever! high revving small block is lighter and car handles better with same tire torching power from Nick's magic. Welcome back George😀

Dana "60" Glass. Keep bringing these giant killers

Nick, one last thing. I believe the idle speed for the 71 340 engine is 900 rpm. It's too cold to go out in my garage and check. It's on the emissions label on the inner fender. Should be in your old Chilton books. They're pretty accurate. Sounds good. One last item missing is the idle solenoid. It sets the idle and the carb screw you're using is backed off a turn so it doesn't diesel when you shut it off with the 900 rpm idle. It let's the primary close completely.

Your thermo quad guy should have told you that you cannot hold the choke open with a zip tie because that locks the front and rear barrels together and holds the secondaries slightly open causing either flooding or an excessive lean condition depending on where it gets stuck. When you test these carbs on the dyno install the factory thermistor choke unit on the intake and connect it to the primary choke linkage just like it would be in the car and you should have no issues with lean or rich readings. I've been rebuilding my own and super tuning thermostats for 30 years, they are the most tunable and reliable carbs

Nice to have a 340 on the Dyno.

A restored '71 Duster 340 recently sold at Mecum for $159K. That blue one your working on is worth a fortune. You better get ready to do more Thermoquads.

Yep, brings back memories of the good ole days and my first cars back then. Great video Nick and George, she runs like a Swiss watch!

Man that’s a lot of snow! I’ve never played with a thermoquad but it seems they like the simple mechanical world. Electric chokes are nice, but there’s something about the old mechanical setup that’s just easy to understand. Thanks for bringing us along on this one, I hope everyone is feeling better.

We have some snow which was not bad. Like 13 inches. Then we got the wind! BUT WOW!! You got some snow. The last 2 wind storms we got with that much snow I would not be able to get out of my house. Good luck Nick and glad you’re feeling better. I hope you get that killer 6 on Dino soon.

That thermoquad is bringing back bad memories of the carb on my 440 back in the day 😆. 76 Dodge Coronet Persuit

Hey Nick, Greetings from Hong Kong. Thanks for another great video.......a little taste of home while I'm on the other side of the world. My Cougar is in Napanee Ont for a new paint job, looking forward to driving it back your way.

Nick, you are correct to suspect the choke pulloff linkage - on Thermoquads, the choke pulloff diaphragm acts as a damper for the secondary air valve. There is a Thermoquad manual on line in .pdf form. As I recall, the 1971 Thermoquad had a different Idle setup from the 1972 and later versions, many folks back in the day would pull the '71 unit off and install a '72 and later carb.

George!!! Glad to see you doing and feeling BETTER!!! This brings back memories of my carb rebuild days, and having to set choke pull-off and unloader adjustments. Love Nick's persistence to get the job done, and done right. Kudos all, and great week to you!!!

By '71, engines already had their air/fuel and ignition systems highly altered for driveability and emissions. Without all those components on the enigine and working correctly, all you will be doing is chasing your tail. Choke stove, heat riser valve, proper aircleaner housing and hoses, ... Watch Nick chase his tail with an emisssions era carb. Connect the factory water pump and thermostat. The engine needs to see that load at low speeds for proper throttle plate opening and idle mixture screw settings.

Hi Nick & George, I Hope that you are feeling better now that the weekend has passed. I love seeing the 340 on the Dyno, and was very impressed with the numbers this stock rebuild made. The Chrysler engineers knew what they were doing, and the numbers don't lie. I loved the video, and am looking forward to the next 340 on the Dyno!

Brings back memories..... 1971 Dodge Demon 340 automatic. Tried to get personalized license plates back in the day that spelled 'Demon' and was denied for religious reasons? Damn, I miss that car!

The ol' hammer handle trick to advance the timing!😂

Nick says here we go. Sure enough commercial comes on

I ran a 71 340 with a TQ for many moons, many-many moms ago. I'm pretty sure you explained you don't know exactly y how it's auto choke works without saying it. You'll find the hi idle ain't high enough at the next cold start. You'll have to mash the gas all the way down to engage the auto choke. It also anticipates your throttle blip to disengage it. You'll know it's ready for blip when it starts to idle higher. : )

340s underrated engine! I think partially because everyones else is looking at 383 440s, 426 hemis, or other 427s 400's 396's even fords big blocks, they didnt really look at 340. Ive seen how they rev through ranges near instant and its awesome! edit: I remember driving home from car show. engine was smoking, i was thinking" oh no." but the smell was different, I was more concerned because it smelt like plastic melting. I pulled over at sheetz gas station away from pumps. i looked around. I kept looking for plastic "whatever" that may be bubbling. then my dad caught up behind me., My dad then looked underneath. it was a shopping bag sucked in and bubbling/burbling on a header. No matter how much we scraped the burnt plastic off. it'd smoke for months, well, we didn't drive the car much to begin with. we covered the scent with grape scent for interior lol

That big spacer under the carb is important too!

Well done Nick! It’s so awesome to see a master of his craft….doing exactly what he loves! Cheers from Melbourne Australia!😀

I'd love to see you do a 340 with a 6 pack.

These guys love their work!

You know Nick Carbs can be like that I rebuilt the 1bbl Rochester in my truck worked like magic for the first year went on vacation started it up and started to puke out past the accelerator.

71 thermoquad was a one year only..Had to get NHRA permission for a replacement in superstock

I live in Vermont lake champlain. Just south of the border. I would like to take a trip up there to see Nicks shop! Love the show guys!

There certainly is no limit to the tips and tricks in tuning offered here. And a fair amount of consensus as to what the problems are. A lot of people don't like them and a lot of people saying how good they are when running properly with everything adjusted right, (and all the parts on properly) Here is a summary of the comments I've collected from this video, specifically aimed at TQ carburetor tuning: As to your lean condition the metering rods came from the factory set to low. There is a screw adjustment on the power piston under the red clip that you can adjust to clockwise to raise the metering rods to richen the mixture . do this at 2100 rpm. As you raise it the engine rpm will increase. I always set it to 1 1/2 % co at 2100 as my Allen Smart Scope had a 3 gas analyzer but did not give A/F ratio. The other problem you have is that your air door spring is set to loose. You will probably have to tighten by about 1/2 turn. Also on the street the accelerator pump needs to be adjusted to give about 1/32 inch more stroke than what the spec is. One other thing you can do is install a quick curve kit in the distributor, the factory curve is way to slow. Unfortunetly Mopar no longer sells this kit but a Mr Gasket kit might work. As for the not returning to idle check that the secondary plates are closeing completely when you go back to idle. Make sure to adjust accelerator pump travel to maximum. No slack! The the air valve, loosen till drops (make sure to keep screwdriver tension so dont unravel) and then turn back tension about 1.5 or so after valve closes. Better to have more tension than less. The plastic phenolic center bowl section can and was alot of trouble as these carbs aged on hot engines . Remember this carb was also used on the terrible Chrysler LEAN BURN engine control systems . The engine heat really was the enemy of the thermoquad and warped the center phenolic bowl assembly . Like them when they work , hate them when They don't. Id only run that carb if you absolutely had to have the car and engine completely original . had a 71 Road Runner 340 Air Grabber, with a Thermoquad , I loved that carb. The secondary air door needs to be set firm. I believe the idle speed for the 71 340 engine is 900 rpm. It's too cold to go out in my garage and check. It's on the emissions label on the inner fender. Should be in your old Chilton books. They're pretty accurate. Sounds good. One last item missing is the idle solenoid. It sets the idle and the carb screw you're using is backed off a turn so it doesn't diesel when you shut it off with the 900 rpm idle. It let's the primary close completely. From decades-old, possible flawed memory, the distributor vacuum advance nipple was always connected to the "ported source" (shown plugged here) nipple on the left front of the carburetor whereas the nipple at the rear of the carb, that it is connected to here, is manifold vacuum. Don't recall ever seeing that on these early non-emission control TQ carb engines. A minor linkage adjustment likely is hanging the secondary throttle plates open very slightly after a wide-open excursion of the main throttle rod. The relation of the primary choke rod is very critical to that whole operation, as the secondary throttle plates are blocked closed when the choke is on any little bit, and that can work to the opposite when not adjusted correctly. We battled and solved many-a Thermoquad issue right out of the factory back in the day thru good old trial and error. God, I'm old... Efaristo, kai na eisai panta kala! PS: Wanna talk about needle seats for the floats backing out in the cover, and other anomalies? Let me know... lol Show less Lean primary operation was built into the carb . I always ran into lean running on these carburetors and the rag on the carb covering the airhorn completely and engine is not choked off tells the tale . theres several adjustments.....i see two thats fighting you here....the spring tention on the rear air vane isnt wound tight enough...changing the tention can fine tune the mixture......the second is the needles....a small screwdriver adjusts the hight of the needles....whoever rebuilt that carb didnt properly set the air valve tention and set the needles to the stock height.... Not surprised it's running lean at idle. My '72 340 with a TQ was very lean from the factory and had to richen it up to get it in the ballpark. Also I noticed the secondary air door seemed very loose earlier in the vid but didn't seem to be an issue when you did the pulls. Thermoquads run like a champ when they are dialed in. Floats would get saturated and flood the bowl. the center screw for the metering rods connects to a manual cam to be adjusted to the work being done, You can adjust the screw to bring the manual over ride sooner or make open later or just work off of the vacuum. Secondary air door spring tension needs tightened Secondary linkage was binding causing secondary throttle blades to not close .I have built and modified many of these no mystery just a design most mechanics are not familiar with. Adjust the metering rod tree! Small flat blade screwdriver, turn clockwise to lift the metering rods up to richen the primaries!! Nick, you are correct to suspect the choke pulloff linkage - on Thermoquads, the choke pulloff diaphragm acts as a damper for the secondary air valve. There is a Thermoquad manual on line in .pdf form. As I recall, the 1971 Thermoquad had a different Idle setup from the 1972 and later versions, many folks back in the day would pull the '71 unit off and install a '72 and later carb. All I can think of with the lack of fuel is that the filter is in backward. I was sitting here yelling "stuck float!" yep! Me too I was thinking no gas in the tank. I remember having to run the air cleaner to get the idle right back in 1971 We called them thermobog carbs at dodge haha . plastic don't like heat . That tiny screw in center if carb. Turn so backs out and up quite a bit. There is also a stop tab on the air valve you will need to adjust with a needle nose. I also [have] the black phenolic 1" carb spacer on my 440 to help keep it real cool. The spacer i had was on one side molded for a spread bore. The other for standard 4 barrel. I highly suggest using that. You can learn to master the thermoquad if your patient. Its not difficult. I drilled all my jets 1 size bigger on drill bit. Did all the right adjustments and ran so crisp and flawless with no stumbles or lag ever! Also, there were 2 thermoquad styles, lean-burn(with lean burn vacum port) and non lean burn. Scarf these up for cheap at swap meets then use the best non warn parts from them to make one great one. There is an aftermarket heat riser choke that has an electric heating element for engines that don’t have a heat door in exhaust manifold I put one on a 360 la in my motorhome and it works so much better than just relying on engine heat

Awesome Nick & Niko《☆》I like 340s with stock HiPo exhaust manifolds👍🏾🥤🤳I put a manual Choke on my 73 Dart Sport 360 when I upgraded to a bigger Carburetor. Welcome back George✌🏼😎☯️

Great job Nick....nice to a Thremoquad on the dyno...good content and thanks

The good ol Carter thermobog.