So all three main sections of Good Carb are washed and drying on the bench. I dunked them each in Simple Green for a couple of days and then scrubbed them with a toothbrush, and 99% of the crud came right off. After a rinse with warm water, they look close to brand new. I’m going to let them dry completely and then start tearing down and replacing parts next week.
I reassembled the stunt carburetor I’ve had sitting on the bench since the end of January and put it aside so that I could tear down the good one. Actually, Jen needed the box that the rebuild kit came in for something, so I figured I’d straighten up the bench while I was moving the parts around. Once I’d gotten that put back together, I looked over the good one and started pulling it apart. I was pleased to find it’s in really clean condition, with a little dust in the phenolic bowl, a tiny bit of corrosion around the air horns, and a lot of clean metal everywhere else. The floats are almost brand new (but will be replaced with brass) and the internals are all clean as a whistle. There was a little leftover gas trapped in the horn that made the basement smell, so I moved it out to the garage this morning, where it’ll get a good dunking in carb cleaner.
When I was a kid, I spent countless hours of my life building with LEGOs on the floor of the family room. I’d build something, take it halfway apart, put it back together again, and then repeat that cycle until I got it just the way I wanted it. All of this was unwitting practice for my adult life, where I’ve disassembled computers, electronics, power tools, engine parts, and other assorted machines without fear of being unable to re-assemble them.
So, working my way through the videos I’ve downloaded, I decided I’d start disassembling the dirty unit first to get my practice in.
Most of the linkage came off relatively easily, and when I understood the secret Thermoquad disassembly trick (two hidden screws under the primary butterfly) the whole thing came apart pretty easily. It was then when I understood why it was so filthy. At some point it had gotten a lungful of water or mud, because both chambers were full of brown crud. The underside of the resin bowl was filled with corrosion and blackened carbon. I began to get nervous, thinking I’d never get it cleaned up.
Into a bucket of concentrated Simple Green it went, and after about an hour’s soak the resin bowl came out looking brand new. I scrubbed it with a toothbrush and bottle cleaner to get the residue out, and let it dry on the bench.
Then I threw the top air horn in to let that soak. Corrosion had crusted over everything made of ferrous metal; the float arms were rusted solid. The whole thing looked charred and sooty. I figured I’d try the detergent to see how clean it would get first.
After about two hours I was shocked to find it had turned Simple Green to Simple Brown, and most of the soot had disappeared. The aluminum appeared much cleaner, and the metal parts were more visible.
It’s still pretty fucked up, though; Simple Brown can’t dissolve whatever that white crusty stuff is in the upper left, and the well under the float (that black square thing on the left) is filled with it. It’s going to soak overnight, and then if I can’t get the parts free I’ll put on some gloves, take it outside, and hit it with the carb cleaner.
Santa (technically, my sister’s boyfriend) brought me a lovely gift this Christmas: a carb rebuild kit for my spare Thermoquad including all of the gasketry, springs, and other small parts needed to overhaul the mechanical bits. Introduced by Chrysler in 1969, the Thermoquad is a four-barrel carburetor designed with two small primary and two large secondary bores. At idle or cruise, the primary bores supply fuel to the engine in small amounts for efficiency, and under load or acceleration the secondary bores open up to dump fuel into the engine, adding power. It’s built around a phenolic resin chamber sandwiched with two aluminum plates, which was supposed to keep the temperature of the upper bowl 20˚ lower than standard metal carburetors of its day–because vapor lock was standard equipment on a 440 big block. So I’m going to have to study up on this Malaise-era marvel of engineering.
My engine, near as I can figure, is a 1979. As the 70’s wore on and emissions standards got stricter, engine displacement decreased and smog equipment strangled engines. IH trucks weren’t as strictly governed as passenger vehicles of the era (trucks over a certain weight and load limit were exempt from CAFE regulations, hence IHC advertising the Scout as the XLC in 1975 onwards) but smog equipment was still added to pass emissions tests, and the carbs got more complicated as the decade drew to a close. The Thermoquad sprouted all sorts of ports and valves and complicated linkages to govern choke, temperature, airflow and throttle, and the result is a lump of metal that looks like C-3PO screwed a pinball machine.
I’ve got three Thermoquads in my collection. The first is the one that came on Peer Pressure, which I had overhauled by my friend Rodney a few months after I got the truck. Tracing the serial number (9128S), it was originally made for a ’79 IHC 345ci engine with an automatic transmission. Rodney is a gearhead of the first order (he has a slingshot dragster parked in his driveway) and no stranger to carburetors. He made it sing, but that was eight years ago.
The second is a spare I picked up from a fellow north of Baltimore. This too is a 9128S. It’s the spitting image of the one on Peer Pressure, minus the funky extra linkage on the throttle arm to the left. It’s also the rebuild candidate and the one I’ll be working with here.
The third is a spare I picked up from my friend Jason, who converted his Traveler over to fuel injection two years ago. Tracing the serial number (9203S), it was originally made for a ’79-80 IHC 345ci California smogged engine with an automatic transmission. The top of the air horn at the fuel inlet is different, and there is one vent tube where my other carbs have two. It’s also super crispy and in need of a major wash. It will be my bench reference and possibly a source of spare parts.
The first order of business is to arm myself with knowledge. I downloaded a series of getting-to-know-you videos from YouTube where a gentleman steps through the features of the TQ, and another where he goes through the steps of rebuilding one. I’ve got the original ’72 Chrysler TQ service manual, an updated ’82 Federal Mogul manual, and the Dave Emanuel bible.
The first order of business is to clean them both, which will require a bucket of Simple Green and a couple cans of carb cleaner, which I’ll pick up this weekend. Then it’s on to the teardown.
Wow, I actually knocked a lot of stuff off the 2018 to-do list. Tires, Hagerty insurance, and Hydroboost are all some big accomplishments compared to years past. I’m feeling pretty good about everything, and Peer Pressure is running strong. Still, there’s more that can be done:
- Buy a new aluminum radiator and install it. Climbing the hills out of West Virginia I noticed the temp gauge climbing perceptibly, something I’ve never seen it do since I replaced the water pump 9 years ago. The overflow bottle isn’t hooked up because the nipple at the filler neck came unbrazed years ago, and the cooling system needs a flush anyway.
- Oil and gear oil change. It’s been 8 years since the first one, and even though mileage is low, she could use some new fluids. This time I’m going to put Rotella 15W-40 diesel in, for the additional zinc.
- Sandblast, paint and install my spare set of valve covers. I’ve got a truck valve cover set with a long filler neck, and now that the Hydroboost is installed I can actually use them. This will make the addition of oil easier (and cleaner).
Buy caster shimsand install them. There’s more work to do to fix the new steering issues.
- Fix the heater linkage so that the heater actually shuts off. The valve in the engine compartment is stuck open, and needs some work to loosen up.
- Fix the windshield wiper motor mount and linkage. The wiper arm on the passenger side is too low and strikes the edge of the windshield, and the whole thing is very slow.
- Buy a 4×10 speaker and install it in the dash. So that I can hear the stereo at speed.
- Re-route the speaker wire. This has been needed for 9 years.
- Rebuild the spare carburetor (finally).
- Buy a hood gas strut and install it. It would just be so much easier to open and close the hood this way.
Since May of 2009, I’ve put 9,436 miles on the Scout, according to the odometer. This is not accurate because the ratio gear on the odometer hasn’t been adjusted for larger tires (so, for example, 50mph indicated = 63mph). Doing a little back of the envelope math for the actual ratio (6 : 7.7) tells me that the actual mileage is somewhere around 12,100.
In that time I’ve spent a total of $3449.51 in parts and labor, or an average of $383.28 a year in maintenance (not including fuel, fluid top-offs, or horse-trading for parts or repairs).
The trip to Ohio was 982 highway miles (via Google), plus maybe 10 miles of running back and forth through Troy to and from the hotel. I’m figuring about 11mpg based on our consumption and Peer Pressure’s limit of about 8 gallons per fill-up. This isn’t as good as Chewbacca did (14mpg with the top down) but I’m running a bigger engine, bigger carburetor, and bigger tires on Peer Pressure.
I got the accelerator cable in on Friday, and after breakfast on Saturday morning I went outside to put it in. It’s fairly straightforward and went in without too much hassle, once I realized the loop molded into the cable wasn’t supposed to hook over the top of the bracket, but used to screw in (and provide room for adjustment) on the bracket itself. The cable hooked right up, and in about 10 minutes I was ready to fire it up and go for a test drive. But when I put the clutch in, the engine revved.
It turns out this isn’t an uncommon problem; what happens is that the cable is too tight on the carb, and the clutch linkage at the pedals travels up the firewall right next to the accelerator. When I push the clutch in, it forces the throttle linkage backwards, revving the engine. Problem is, I’ve got no play at all on the bracket. The cable is pushed as far forward (towards the carburetor) as possible; there’s nothing else. The arms on the carb aren’t adjustable, and there’s no other allowance for adjustment in the cable itself.
I looked in the fittings and bracketry that came with my second engine, but there’s no spare there. So I’m going to fabricate a U-shaped piece of metal with two holes. One side will go on the bracket and the other will hold the cable, and I’ll build in room for forward adjustment.
In other news, Finn and I drove to White Marsh to visit a guy who had an original IH Service Manual for sale on Craigslist. I have the new reprints from Super Scout Specialists, and they’re great, but I couldn’t pass this up. It’s softbound but 3-hole punched, so now I’ve got to keep my eye out for a 1 1/2″ red binder to put it in.
In doing the preliminary research on my carburetor, I stumbled upon a 16-part video series detailing the process of rebuilding a Thermoquad, which I downloaded for future reference.
I don’t have any money to be spending on the Scout right now, but one of the things on the to-do list is to rebuild a spare carburetor. I have two spares, one of which is of uncertain provenance and the other a direct pull from a Scout. Given that Carter made a million modifications to the Thermoquad over its lifespan, I thought I’d put the spare side by side with my working carb to see what visual differences I could pick out.
Apart from the extra arm attached to the main throttle linkage, they look identical to me. I did a brief comparison to my third spare, and that one isn’t even in the same family. The main body is cast differently, and there are a handful of inlets and outlets that don’t match up to the ones I’ve got, or are completely missing.
From what it looks like, most carb rebuild kits are ~$50. Peer Pressure has been getting harder to start reliably, so some carb adjustment is definitely moving up the priority list, and having a pair to tear down will help in familiarizing myself with these complicated beasts.
Peer Pressure is back on the road and running like a top. After a long three weeks at the mechanic, the carburetor problem was finally solved; the reason for the leakage was a set of tiny O-rings which were actually supposed to be X-rings. Once he’d torn it down for the fifth time and put them in, she buttoned up and ran like an excited puppy at the edge of an empty field. I’ve had her out on several junk runs, a trip to the Home Depot, a trip to Columbia, and into Baltimore City on a day with record-setting heat, and the temp gauge stays obediently on the left side of the indicator. She starts with one twist of the key and idles like a satisfied kitten. Best of all, the obnoxious stink of gasoline and rich exhaust is almost completely gone—there’s less exhaust backwash on this truck than there was on Chewbacca, as a matter of fact.
I got word from my mechanic yesterday that the carb went back together well, except for one small hitch: the gasket they sent in the rebuild kit (Walker 15821A) is too thick for this application. Apparently I have a heated choke (as opposed to manual or electric) which means the choke is actuated by the temperature coming off the manifold. Some good information on the various methods of automatic choke actuation can be found here, as well as some Thermoquad-specific information here.
With the thick supplied gasket installed, one of the linkage rods isn’t long enough to reach, so he had to call around to find the correct gasket and have it overnighted for tomorrow—which is great, because we can’t pick it up until tomorrow evening anyway.