Demon Carb
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Demon Carb

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    Member CashLeak's Avatar
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    Default Demon Carb

    My 78 Nordic has a thermoquad carb on it I cleaned it and put a kit in it but it still has flat spots and acts like it running out of gas when you punch it at 3000 rpm. I found a 750 Demon carb on CL for $200.00 Is the demon as good as a holley or should I just step up and buy a new 750 Holley Im running a stock marine 454 (I think ????? ) with a torker 2 intake and logs and risers Thank you in advance for you help

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    Senior Member bp298's Avatar
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    Quote Originally Posted by CashLeak View Post
    My 78 Nordic has a thermoquad carb on it I cleaned it and put a kit in it but it still has flat spots and acts like it running out of gas when you punch it at 3000 rpm. I found a 750 Demon carb on CL for $200.00 Is the demon as good as a holley or should I just step up and buy a new 750 Holley Im running a stock marine 454 (I think ????? ) with a torker 2 intake and logs and risers Thank you in advance for you help
    which demon is it? I've been running mighty's for 12 years. you may still have to tune it, but they work just fine.

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    RPB
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    have a race demon on 71 bronco 396W stroker....less maintanance and fuss than anyother carb i own, doesnt mean its better just low maint for me.
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    demon 750 here on my mild 454. no problems.

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    Village Idiot fc-Pilot's Avatar
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    I have had five or six. Just like any other Holley based carb, if they are right, they will be fairly trouble free. If they are wrong, well then they are just wrong. They had some quality control issues for a while and two of the carbs I got fell victim to that. Once I figured out what was wrong I got it fixed and we were back up and running.

    Paul

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    Senior Member 74Bonneville's Avatar
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    Quote Originally Posted by CashLeak View Post
    My 78 Nordic has a thermoquad carb on it I cleaned it and put a kit in it but it still has flat spots and acts like it running out of gas when you punch it at 3000 rpm. I found a 750 Demon carb on CL for $200.00 Is the demon as good as a holley or should I just step up and buy a new 750 Holley Im running a stock marine 454 (I think ????? ) with a torker 2 intake and logs and risers Thank you in advance for you help
    I think there's missing information here. How long has it been running bad? There was a progression of running well to what it's doing now. Did this happen all of a sudden? Have you checked the simple stuff first? Fuel filters, water separators, fuel pressure ...

    If it really is the carb it may be better & cheaper to take it to a good carb shop rather than replace it with a used one.

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    I bought the boat about 2 months ago. The boat had been in storage inside for 11 years . I drained the tanks replaced the fuel lines and filter cleaned the carb and put new kit and floats in it . My main reason for wanting a holley based carb is because they are easier to work on (for me) . No metering rods no plastic body . As far as a base line for how it should run I have no idea it didn't run when I got it . I just trying to get a dependable boat that runs in the 50 MPH range and doesn't leave me in the middle of the river in need of a tow !!!

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    Senior Member 74Bonneville's Avatar
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    Quote Originally Posted by CashLeak View Post
    I bought the boat about 2 months ago. The boat had been in storage inside for 11 years . I drained the tanks replaced the fuel lines and filter cleaned the carb and put new kit and floats in it . My main reason for wanting a holley based carb is because they are easier to work on (for me) . No metering rods no plastic body . As far as a base line for how it should run I have no idea it didn't run when I got it . I just trying to get a dependable boat that runs in the 50 MPH range and doesn't leave me in the middle of the river in need of a tow !!!
    Good reason to start replacing stuff

    I know I would, get it reliable

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    gn7
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    Quote Originally Posted by 74Bonneville View Post
    Good reason to start replacing stuff

    I know I would, get it reliable
    I can't say I blame him. The Thermoquad is not the best carb I can think of. If it wasn't for Chrysler, not sure Carter could have sold more than 6 of them. As a marine carb, its just fire looking for a place to happen.

    I can't imagine anybody installing one under an engine hatch, but if it is, get something else, anything else. Even a BG Demon rebuilt by a 5 year old.

    The major problem with a thermoquad is, 99% of them were built as emissions carbs. Its not surprising that you have a flat spot in the midrange when accelerating. Chances are its an air door issue and you'll play hell trying to get rid of it. If it was worth it, I would tell you to take it to a carb shop and have them rework for performance use, but most carb shops don't care to deal with them. Even ones that specialize in Q jets and Carter AFBs, and if you find one, the cost will be more than a new Holley 750 Ultra HP.

    Like BP posted, the Demon came in a couple different models, not counting the King Demon, there is a Road Demon and Race Demon, and the Road came in vacuum secondaries and mechanical double pumpers.
    Not enough info, except to say, anything is better than what you have.



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    Member CashLeak's Avatar
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    I agree the thermoquad is gone I have a edelbrock 750 loaner on for now while I wait for my holley 750 DBL pumper. But now I think I may have a new problem. Thanks everyone for your help!!!

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    Member CashLeak's Avatar
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    Oh I didn't by the Demon its a Barry Grant Demon 750

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    Quote Originally Posted by gn7 View Post
    I can't say I blame him. The Thermoquad is not the best carb I can think of. If it wasn't for Chrysler, not sure Carter could have sold more than 6 of them. As a marine carb, its just fire looking for a place to happen.

    I can't imagine anybody installing one under an engine hatch, but if it is, get something else, anything else. Even a BG Demon rebuilt by a 5 year old.

    The major problem with a thermoquad is, 99% of them were built as emissions carbs. Its not surprising that you have a flat spot in the midrange when accelerating. Chances are its an air door issue and you'll play hell trying to get rid of it. If it was worth it, I would tell you to take it to a carb shop and have them rework for performance use, but most carb shops don't care to deal with them. Even ones that specialize in Q jets and Carter AFBs, and if you find one, the cost will be more than a new Holley 750 Ultra HP.

    Like BP posted, the Demon came in a couple different models, not counting the King Demon, there is a Road Demon and Race Demon, and the Road came in vacuum secondaries and mechanical double pumpers.
    Not enough info, except to say, anything is better than what you have.
    I could not agree more! The thermo carb is a phenolic body and if it sat for 12 years I believe you would save money replacing it! Especially if it was in storage in a non climatic controlled area. I don't know anybody that likes those things other than somebody doing a factory original restore!

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