You don't want to go with a '71 ThermoQuad. That's the non-"solid-fuel" version, which is quite different internally due to the strange way in which fuel is metered in that year only, which involves bleeding air into the metering circuits prior to introduction into the venturi. They're not exactly what you'd call easily tuned or particularly good-running carbs; "tweaky" or "finicky" would be better descriptions. No big deal, though, since being 340 only, they're virtually impossible to find. In '72, the TQ got better metering circuits and also showed up on the 400 high-perf and all low-performance/C-barge 440s, but it's still not easily found.
However, in my experience, most TQs are useful as-delivered. Yes, you want the vacuum advance port but 4V trucks have that port almost universally during the TQ era. If you do have one without it, though, there are ways around it. One is to install the timed port yourself and the other is to use a throttle-actuated vacuum switch. The work to install the timed VA is almost done for you other than drilling a couple of holes (you will need a pin-vise drill and a tiny bit, both cheap) The electric vacuum switch can use the original idle switch found on ESA/ELB* carbs. Mopar used to make an electric vacuum solenoid, part number 4145181, but there are commonly-avaliable 12V solenoids that can replace it, such as Ingersoll Rand #P251SS-012-D. Neither option is particularly difficult.
Looking at Monkeyed's carb, the only wire I can definitively see is the one for the bowl-vent solenoid which also feeds the electric choke heater used on the carb's original application. That wire simply goes to 12V+ switch (key-on), so wiring it is a snap. All it does is close the carburetor's bowl vent when the key is switched off. Nothing magic about it, other than keeping the gas smell out of the garage. If you get me the list number, Monkeyed, I can tell you exactly what you've got there. The number will be stamped on the carb's mounting flange on the driver's side, facing the firewall. I can also tell you the CFM rating of your carb at that point, though they only came in 3 sizes: "large", "huge", and "now you're just being silly", also known as 800, 850, and 1,000CFM flow ratings. The 1,000CFM unit was never used by the factory and is readily recognized by the raised pads above the float bowls that say "Competition Series". No, none of these carbs is "too big" for your engine; that's the magic of the ThermoQuad. Tune it to spec and it's a perfect fit every time.
Rebuilding the TQ is pretty straightforward using just the instructions with your rebuild kit (
do not order a carb kit any other way than using the list number, ever!). One big area of concern being the two square-section O-rings low in the carb. They seem almost useless, but if you forget to install them, the carb will literally dump fuel into the engine. It will run, but it'll run quite poorly. I'm sure I'm not the only one here who's made that mistake. Trust me, you'll only make it once. Pop the extra few bucks and get a new pair of floats while you've got it apart. It's cheap insurance. Brass & nitrophyl will interchange willy-nilly, and though in my experience people seem to prefer brass, today's nitrophyl floats are virtually impervious to fuel soak and will last nigh-on forever.
Even ESA/ELB carbs are jetted fairly rich from the factory so tuning is pretty simple. The only real "trick" to a ThermoQuad is the secondary air valve adjustment, which can be done with 3 screwdrivers if you use a little intelligence, but the factory-type tool is easily made or readily gotten via sources such as eBay. Setting up the carburetor per the factory's '72 guide will result in excellent performance in all aspects: fuel economy, drivability, and those full-throttle dances that remind you why you wanted a four barrel in the first place. Click
here for the table of contents; I highly recommend you print out each and every page (they're clickable in the table of contents) and set your carburetor up exactly as shown, including bending the linkages, etc. Yes, it all really does make a difference. Another tuning guide, perhaps a little less comprehensive but easier to print, can be found
here. Whichever you choose to print for garage/driveway use, you'll want to have it laminated because once you fall in love with the TQ, you're hooked and you'll want to have this information forever.
One last tip, and this goes for everyone running a carburetor (meaning virtually everyone here):
Today's gasoline is absolute crap. You don't have to be told about ethanol blends as high as 10% (E90) Carburetors don't like that at all. It varnishes quickly, tears up seals, diaphragms, etc. For the best performance, economy, and longevity from your carburetors, I cannot stress this enough: Use Lucas Fuel Treatment #10020 (single-serving) or #10003 (quart size) about every third fill-up, and use Gold Eagle Marine Sta-Bil (#22239 treats 80 gallons, #22240 treats 320 gallons) or Sta-Bil Ethanol Treatment #22275 (80 gallon size) all the time. The Marine Sta-Bil is the better of the two Gold Eagle products but both work quite well. I don't work for, nor do I sell either line of products, but years of experience with ever-decreasing fuel quality have taught me well by not only personal experience but by listening to my customers. If you're a believer in SeaFoam, well, so was I. You will go back and throw rocks at SeaFoam after using the less-expensive Lucas product, and the Sta-Bil products convert your ethanol-polluted fuel back to nearly E0 while SeaFoam is virtually ineffective. This will not be the last time I rant about these products; they truly make a ton of difference. You will notice a difference in how well your car runs, I promise.
* ESA = Electronic Spark Advance, which is the later term for ELB (Electronic Lean Burn)
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