Carter Thermoquad on a 350

[BlouDon]

I bought my truck with a Holley 1850.

The engine did not idle happy and I was convinced, based on fuel consumption, that it was running pig rich.

I had a spare Carter Thermoquad (the cousin of the Rochester??) lying around that came of some Mopar 440, which I had fitted to and tuned on my Jensen Interceptor (also fitted with Mopar 440).

I know the Carter has a very poor reputation but I recon its the Rolls Royce of 4 barrel carbs.

The elegance of the TQ is that, after removing the air filter:

• Idle mixture can be tuned by hand;
• Primary mixture can be tuned with a small flat screwdriver;
• Secondary mixture can be tuned with a smallish long nose pliers.

My SBC was fitted with the Chevrolet Performance 10185063 spread bore intake manifold which allowed me to bolt the Carter straight on, using a 3mm (1/8") self made cork gasket - which also has gasket running down the middle of the carb over the seperator. Only trouble is that I have no choke operation - yet.

This carb improved matters a lot but I was still not happy. Anyway, I had to repair an intake manifold coolant leak above #8. The Felpro gasket kit I had, also included EGR, blanking plates to reduce the EGR ports with smaller round openings. In our hot climate I would have preferred complete blocks, but there we are.

Since I had the intake manifold off, I noticed that there were round openings in the bottom of each plenum about 8mm (5/16"), allowing exhaust gas back into the plenums. These I also blanked off by tapping 12mm thread into them and installing bolts with Loctite 272 thread locker.

All this has improved matters significantly. She now idles nice and steady and really sounds happy at part throttle.

Next project: Out with TH400, in with 700R4.

[Eddie H.]

I rebuilt a couple of thermo quads back in the early 70's. I always thought they were a decent carburetor. I haven't seen one in many years.

[Stocker]

My only experience with a Thermoquad was on an early-Seventies Plymouth Duster I owned for a short time. We could not get it to run right and the concensus was the plastic (composite?) carb body was warped, as they were prone to do. Proper sealing was not possible and vacuum leaks were inevitable. I finally had enough, took a small financial bath, and traded it on a new '79 Honda Accord. One of the best automotive deals I ever did.

[GASoline71]

Been watching Roadkill Garage? There is a cat on there that loves those things.

The 1850 you pulled off will run circles around that Thermoquad when tuned properly to your application.

Gary

[BlouDon]

Until now I did not have choke.

The is because the Chevrolet Performance 10185063 spread bore intake manifold does not make provision for the Carter type choke.

Well, now I have manual choke!

[geezer#99]

Nothing wrong with a thermobog if they run right!
Good thing you have the intake you do have. Secondaries won’t open if you had used a stock cast iron intake.
Hope that manual choke keeps working for you!

[Ironangel]

You might find this interesting, http://www.retrorarities.com/images/...nformation.pdf
The Carter Thermoquad is a "Spread Bore" design like the Rochchester Quadrajet so they can be tuned for excellent gas mileage and go full game on when the vacuum secondary's open up. I rebuilt a Carter "Competition Series" AFB a couple of years ago for a semi-hopped up 350 Chevy and was impressed with the simplicity and ease of tuning because I'm a dedicated Quadrajet man. The TQ's have an advantage in hot climates or when used on them giant Mopar Elephant intakes because the plastic center section keeps the fuel 20 degrees cooler than the AFB's, and they flow more air than QJ's and most Holly's. Gary will likely dispute that but the "little" TQ's were rated for 800cfm and many were rated to flow 1000cfm, to feed HEMI's and 440's no doubt. The phenolic center meant less vapor lock than that experienced with earlier carburetors. The key to finding a good useable or rebuildable TQ is to find one that has a good phenolic center assembly. Many were warped or cracked due to engine overheating or improper fuel-to-air mixture. An easy way to check the phenolic center section is to turn the carburetor upside down and check the bridge or divider between the barrels. This divider should be intact and show no melting or loss of wall thickness. When the phenolic center is intact and sealing, the Thermoquad is a hard carb to beat! PS. Gary will like the last sentence on page 3. All good Gary, I have a new Hollly 750 double pump on the shelf jetted and ready to go in case my BBC Quadrajet quits working...

[rpmerf]

Originally Posted by GASoline71

Been watching Roadkill Garage? There is a cat on there that loves those things.

Steve Dulcich. He doesn't consider himself a Mopar guy, he just has a field of cars and a barn full of parts.