Thermoquad rebuild or not?

Discussion in 'General IH Tech' started by Elwood, Feb 16, 2013.


  1. Elwood

    Elwood Farmall Cub

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    The skinny: I bought a used thermoquad that is in pretty good shape but hasn't been used in a long time. I took to a local carb re-builder for a rebuild and he told me that it wouldn't be worth a rebuild due to the body of the carb (non-metal) being prone to failing and that it is no longer available to purchase. "I can rebuild it for you, but there's no telling how long that body will last. Could be a week. could be a year. At that point you'd be out the rebuild and have to get something different any. Spend a little more on a different carb and be ahead of the game in the long run."

    Did a quick search here and didn't see a discussion on this. I'm curious how accurate this is cause I kinda got the feeling he told me that b/c he didn't want to do. The guy is well known in the area and many shops use him and stand by his work.

    thoughts?
     
  2. Tim Potter

    Tim Potter High Wheeler

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    There's plenty of threads on here about the TQ, including problems with it. TQ's are the like a Greek tragedy, both agony and ecstasy. You'll find those on each side. The float bowl can warp but can be flattened. The well caps can leak as the glue breaks down, they've been reglued and come loose again letting raw fuel flow down the carbs throat. The secondary adjustment can be tricky, if not done correctly they can open late or not at all. There's a ton of info here on TQ's and all its quirks.
    I say the carb guy told you the truth. Unless you're doing the rebuild yourself, it can be expensive and if he's already told you he cant guarantee the carb, you will be better off buying a new carb rather than throwing money at a TQ.
     
  3. mallen

    mallen Y-Block King

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    Depends on what emissions laws you have to live with, I bet you can't find a carb that has been tested on an an international 392 and is on the CARB list. People mention the edelbrock 1400 as being "Street legal" but that's ONLY on a Chevy engine of the right year, But I do agree,if your talking about using it as a replacement or upgrade,there are far easier paths to take. If you can't rebuild a carburetor,you won't understand the pros and coins of the tq. Heck,even a lot of people who are very knowledgeable about carbs don't. Some people will tell you the TQ is plagued with design flaws,while others will say it was years ahead of its competition and the most advanced carb ever built. They are both right. If it haven't been for fuel injection,I think most cars would have derivatives and descendants developed from that design.Plastic are much better today for instance and I bet there are much better options than phenolic resin. Of course once we had cheap powerful computer controlled fuel injection, all those complex mechanical devices ended up right next to other obsolete and overcomplicated devices like WWII clockwork missile guidance systems.
     
  4. 1975IH200

    1975IH200 Y-Block King

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    Carter Thermo-Quad Carburetor:

    I like the Carter T-Q and currently run one on my 392 engine in my truck.
    The TQ is very tunable and adjustable in my experience. It has a reputation for being a "bad" carb: bogging, hesitation, leaky, difficult to adjust (tune) to an engine, etc.
    There is the eternal question about the 'plastic' fuel body and the belief that they warp easily, or will warp soon. I have never seen a warped TQ body that had not been abused by someone trying to disassemble the carb without proper knowledge.
    Properly rebuilt and tuned for your engine/truck, it should start and idle at any temperature, cold soaked or heat soaked, assuming you use proper starting procedures for carbs, (not Fuel Injection). Starting Instructions are in the IH Operators Manual for your vehicle.

    So I would strongly suggest if you are contemplating running a T-Q on your IH engine, then first, learn about it.

    Thermo-Quad Knowledge Sources:
    1. A book titled "How to Rebuild and Modify Carter/Edelbrock Carburetors" written by Dave Emanuel. ISBN 13 978-1-932494-36-5 or ISBN 10 1-932494-36-7. Easily found and purchased off the internet. This is an excellent source for carb info in general and specifically for the Carter WCFB (Will Carter Four Barrel), AFB (Aluminum Four Barrel), AVS (Air Valve Secondary), T-Q (Thermo-Quad) and later Edelbrock 1400 series carbs.
    2. Link: http://members.shaw.ca/crussel/thermoquad/tqguide.html Download and print this out, read and study.
    3. Link: http://www.imperialclub.com/Repair/Lit/Master/290/intro.htm. Download and print this out, read and study.

    PARTS:
    1. Rebuild Kit. I use a GP Sorensen part number 96-246C kit, costs approx. $37.
    2. Floats. I use two GP Sorensen part number 779-1726. These are nitrophyl floats. I have found that the brass floats sold for the T-Q will fit the fuel bowl, but are not the correct shape to work properly and could not be adjusted to work properly. The Nitrophyl floats work quite well. Good ones weigh 7.5 to 8.0 grams.
    3. Choke pull-off. Test with a vacuum gauge per the manual, if it fails, replace with new. Some carbs use two choke pull-offs. Check both and replace as necessary.

    BEFORE REBUILDING your T-Q or any Carburetor:
    1. Be sure your ignition system is tuned up properly and is working as it should.
    2. Be sure the PCV system is correct and working properly.
    3. New fuel filter installed and clean fuel source.
    4. Fuel pump working properly, mechanical pump is fine for the T-Q on an IH engine. If running an electric pump, be sure the fuel pressure is correct: 4.5 to 5.5 PSI on a known calibrated fuel pressure gauge.
    5. Vacuum Hoses: should be checked for leaks and replaced if leaking, cracked, brittle or old. Check against the vacuum hose chart for your vehicle.
    6. Carb sitting for years unused or unknown history, ie. not fresh: rebuild it and skip the hassle of trying to get a dirty/grunged/gummed carb to run properly.
    7. Air cleaner housing correct for the vehicle, ie. does it have the heat riser tube/hose form the right hand exhaust manifold to the snorkel? and does the inlet valve work correctly. This is important for cold engine temp operation and warm-up.
     

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  5. FMhouse

    FMhouse Farmall Cub

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    There is no reason to be afraid of the thermoquad.It's a simple carburetor,and once you know how to set it up,will perform great,as long as nothing is damaged.I recently rebuilt one for a dodge 440 project car,and all it needed to run great was a little more tension on the air valve spring.Goes like a raped ape.
    I ran one for years on a 340 mopar with no trouble,and great power.
    Not a bad idea to put in a couple of new floats when you are in there.
     
  6. 2dafloor

    2dafloor Farmall Cub

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    Most old carbs I own its the throttle shaft bushings that are worn creating a leak. All the rebuild kits in the world don't fix worn parts.

    Now what you do for emissions I have no idea.
     
  7. Ristin

    Ristin Binder Driver

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    I'm in the process of rebuilding two thermoquads. I've had some issues and nearly gave up, but when the TQ was dialed in, my truck ran great. I eventually want to go TBI, but there are some many other issues I need to address on my truck first. Because I know I want TBI, purchasing a new carb doesn't make sense so rebuilding the TQ is my best option assuming I can do the rebuild properly.
    I think my issues stem from not having the correct rebuild kit. I purchased the Echlin kit from Napa auto and the gaskets don't look the same. The base gasket is different as well. I ordered the GP Sorensen kit last week and it should arrive tonight. I'll have a chance to compare gaskets.
    I hope to report good news by the end of the week.
     
  8. FMhouse

    FMhouse Farmall Cub

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    I mentioned somewhere before that it's critical to have the proper base gasket on your thermoquad,I once had the secondaries hang open on my 340 due to the wrong gasket interference,and almost grenaded my engine...:oops:
     

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