Holley/Demon Carb stumble

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  1. Cudafever

    Cudafever Well-Known Member

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    Hmm
    well i really did.
    I did because when i called holley about doing this they say point blank that they had no idea if it would work on a BG/ demon car and click end of discussion.

    so i was vary careful with matching the demon gasket with the gasket that came with proform. no differance.
    In fact the only thing that that i notes was when i replaced the main venture. the proform didn't have the power valve drilled out for the secondaries power valve. that main body/venturis can be bolted on either way but the power valve would Not work if you put it on wrong. the demon didn't matter which way you installed it.

    Not saying your wrong and sure could have overlooked something as well.
    Thanks for your response.
     
  2. PRH

    PRH Well-Known Member

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    The first BG carb I bought was the predecessor to the Demon carbs..... the “Claw”.
    It was a Gold Claw, which became the Race Demon RS(removable sleeve) when they changed over to the Demon line.
    Mine was a very early production unit, which still used a Holley cast baseplate and Holley bowls that had the “Holley” lettering milled off, and then re-died gold.
    There was a note in the box stating that when the bowls and baseplates were available they’d ship them to me.
    They would have a call tag with them to return the old parts.

    The new parts arrived some time later, but no call tag.
    I called, they said just keep the stuff.
    Those bowls and that baseplate went on my made from scratch HP950.

    The point of the story is...... BG was using Holley baseplates interchangeably with the billet Claw pieces at the beginning.

    Also, the BG carb kits used to say Demon/Holley right on the packaging.
    I’ve used piles of those kits to refresh Holley carbs.
    So, whatever differences there are in the baseplates and blocks, it’s not something that requires different gasketing.

    I’ll tell you what though...... those Claw carbs often had some manufacturing issues that weren’t going to be “tuned” out of them.
    I have a 750 Silver Claw here that someone gave me.
    I’ve fixed(well..... hopefully fixed) a few issues I found, but have yet to try it on a motor to see how it works now.
     
    Last edited: Mar 30, 2020
  3. yellow rose

    yellow rose Doctor of Thinkology.

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    What kind of manufacturing issues did you find? I really only played with one Demon carb and then that customer went to a flying toilet and alcohol.
     
  4. Cudafever

    Cudafever Well-Known Member

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    You had me question if it was a actual BG carb.

    IMG_2258.jpg

    Yup in small letters
     
  5. mderoy340

    mderoy340 Well-Known Member

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    They are not the same. I wish Holley would of never bought Demon out. Read tech tip #1
    http://corvette-restoration.com/wp-content/uploads/technical_papers/BG_Carb_Setup.pdf
    Tech Tip #1 BG carbs use mostly the same gaskets as a Holley. However, the throttle plate gasket (the gasket between the bottom throttle plate and the upper body of the carb) on a BG has 4 idle fuel transfer holes that are not in the same location as the Holley. If you use a Holley gasket, you will not get any fuel flow through the idle metering circuit on the BG, and the idle mixture screws will not work. You can use the Holley gasket, but you need to slot the idle fuel transfer holes in the gasket to match the holes in the BG carb.
     
  6. Cudafever

    Cudafever Well-Known Member

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    Hmm well if i order another base/throttle from proform, i will look even close at that area. and post up my findings.
     
  7. PRH

    PRH Well-Known Member

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    You have a Demon and Proform baseplate on hand now, no?
    If one were curious enough, and had some time to kill....... they could do a little side-by-side look see.

    The only time Ive run into the situation where the idle feed ports don’t line up between the body and the baseplate was when I’d modify a 750 to use an 850 baseplate.
    When doing that, you had to slot the holes in either the main body or baseplate.
    But that was prior to the arrival of the Holley HP950 carbs.

    I’m not saying whether the Holley and Demon have the holes in the same place or not........ but I’ve never noticed it.
    The BG 190004 kit worked on Holleys, Claws, and Demons......with different throttle bore sizes, so there is a variety of baseplate gaskets in the kit.
    I just matched up which one I needed and forged ahead.
    I never noticed if there were ones that had only those idle feed holes relocated.
     
  8. PRH

    PRH Well-Known Member

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    The most common was the air bleed holes in the main body not being connected where the holes from the top are supposed meet the holes from the metering block side.
    Also issues with the secondary linkage where you couldn’t get the rear blades to sit all the way closed.
    (These were more of an issue with the Claw carbs).
    On the RS models, which have replaceable boosters....... sometimes the counter bore for either the booster flange or retaining nut wasn’t deep enough and would allow the booster/nut to sit too proud of the gasket surface, which could keep the gasket from sitting flush against the body.
    Creating a minor air leak which would erratically affect the tune.
    Often behaving different each time to reinstalled the bowl/block.

    I also ran into booster stake tubes folded over in King Demons(and BG reworked Holley 4500’s) along with some metering blocks that had been damaged during some machining operation...... and they had attempted to repair it with epoxy....... and the epoxy had run into the main well.
    (That was on a brand new King Demon I bought).

    That’s not even mentioning how screwed up a lot of the calibrations were.
    Not that they didn’t match the specs in the catalog...... but how they were calibrated just sucked.

    It wasn’t uncommon at all to mess with one for hours on the dyno, try all kinds of stuff to get it sorted out....... only to bolt on an equivalent ootb Holley....... and have the Holley not have any issues.

    Early on there weren’t very many different models.
    There wasn’t anything “affordable” that had adjustable air bleeds.
    And the Speed Demons often were way way lean, and didn’t idle well with any kind of cam.
    So, I got to where I’d install adjustable air bleeds in them and tweak the tune up before even bolting them on the motor.

    I’d say the one area where BG/Demon really excelled......... was marketing.
    Those big full page ads in the National Dragster and car magazines were pretty convincing.
    The actual product however....... I found to be lacking more times than not.

    The last Demon I was running on anything was an 850DP Mighty Demon I took in trade.
    Apparently it had been being used on a 440 with no luck.
    I don’t know how they arrived at the calibration they had in it(which made no sense at all), but I put some new gaskets in it, put what I felt was a more normal tune in it, and started using it on the dyno.
    I got it dialed in with a little use, then it became a carb I used regularly as a dyno mule.
    It worked well for me for a few years like that.
    I was getting to where I was pretty “carburetor rich”, and figured that would be an easy one to get rid of ....... so I sold it.
     
    Last edited: Mar 30, 2020
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    • Cudafever

      Cudafever Well-Known Member

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      The proform works, and is on my car. The demon is waiting for parts and is only a base plate and center section right now.

      When i get a minute, I will pull the base/Throttle plate back off of the Demon and take a real good look at it.
      more than likely the only way the two will be look at together is if i buy another proform base plate for the Demon. Which may happen down the road.
       
    • PRH

      PRH Well-Known Member

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      Before the original Holley HP950 existed, modifying 750 Holleys to use 850 baseplates was a pretty popular mod in some oval track series.
      I did a few of them myself.
      When doing this mod, as I said earlier...... there was a mismatch in placement of the idle discharge holes between the main body and baseplate.
      If you didn’t correct it, the idle discharge ports in the baseplate were blocked off completely.
      The carb effectively has no idle circuit in that situation.
      So the blades have to be opened up enough to either expose the transfer slots enough to run, or even farther to get the main circuit activated.
      A little tweak to “connect the dots” was all that was required to get the idle circuit working normally again.

      The point being........ even if the discharge holes in the Demon body and the PF baseplate don’t line up....... it should be fairly easily correctable.

      One of my friends decided to do the 850 baseplate upgrade on his 750DP.
      He had overlooked that part of the mod, so of course the motor wouldn’t idle......at all.
      Letting off the gas was like turning the key off.

      He called asking advice....... I knew exactly what the issue was but wanted him to find it himself, so I kept telling him to “follow the path of the fuel”.
      He never did figure it out, and was pretty convinced I wasn’t sure how to fix it myself.
      So, I told him to drop it off with me, I’d fix it..... without telling him how to do it........ and if he bolted it back on and it worked, he’d pay me $50.
      The $50 wasn’t really for the labor so much as doubting me :soapbox:

      Yes...... I got the $50.
       
      Last edited: Mar 31, 2020
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      • Cudafever

        Cudafever Well-Known Member

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        The $50 wasn’t really for the labor so much as doubting me :soapbox:

        :thumbsup::thumbsup:
         
      • Cudafever

        Cudafever Well-Known Member

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        Got all my parts for building my proform fuel bows(remember the Demon fuel bowls are currently on the proform carb.
        There is a lot a parts to build two fuel bowls
        IMG_2260.jpg
        or is a proform???
        IMG_2261.jpg
        seem like i'm all way fighting build tolerances. Had to run the needle and seat in and out of the bowl several time and then had to clean out the shaving in the threads............. installed secondary bowl with no issues but when i installed the primary float into the bowl. The bowl would stick to the top of the float bowl(rubbing) and would stay there until i pushed on it.
        Pull it back out and can see the seam aka the mold seam was of set just a little causing the rub. scraped the seam with razor knife and problem solved.

        two complete fuel bowls ready to go on my 850 proform carb
        IMG_2264 (1).jpg
        Now for the Demon side of things
         
        Last edited: Apr 2, 2020
      • Cudafever

        Cudafever Well-Known Member

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        Separated the base plate from the main body of the Demon today
        I unbolted it and flip the base over. so you know the orientation of it.
        IMG_2262.jpg IMG_2263.jpg

        Don't know why it flip the 2nt picture like that but the gasket is moved from one pick to the other.
        So what hole need elongated on the gasket.
         
      • PRH

        PRH Well-Known Member

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        There are no issues with the idle feed hole alignment between that main body, gasket, and baseplate.
        Everything is lined up.

        But, those are two matching parts right?
        Demon main body + Demon baseplate?
         
        Last edited: Apr 3, 2020
      • PRH

        PRH Well-Known Member

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        Curiosity got the best of me, so I dug out my Silver Claw 750 and popped the baseplate off.
        I haven’t run this on anything since I went through it.
        Good thing...... it wouldn’t have idled.
        This is a good example of not paying attention when putting things back together.

        This carb has a baseplate that will work with the idle feed hole in the body being in the location for either a 1.687 or 1.750 baseplate.
        There is a slot to accommodate either.
        IF....... you run the correct gasket.
        This main body uses a 1.687 baseplate...... but the idle feed hole is in the 1.750 location.
        The gasket that was in there was for 1.687...... and as such, had the idle feed hole in the body blocked off.
        This would have been one of those “no worky” situations.
        A few pics:

        Claw 750:

        F09C5BE2-9E79-432D-B06A-1B5BD6304571.jpeg

        Idle feed holes in 1.750(left) & 1.687(right) gaskets:

        F48A21F5-873C-48EF-A2D4-99942474B9B0.jpeg

        Idle feed holes in main body:

        918AD1DF-B81B-4F61-B909-659126057E9E.jpeg

        Idle feed hole/slot in baseplate:

        2BFF0BA8-ECD2-486D-A87A-A65C567EC604.jpeg
         
        Last edited: Apr 3, 2020
      • PRH

        PRH Well-Known Member

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        Idle feed slot with 1.687 gasket(which is what was installed in carb) on baseplate (hole lines up with slot):

        19ECCA1A-9285-4FBB-99DC-39F91959F135.jpeg
        Idle feed hole of 1.687 gasket on main body(as you can see, the gasket completely blocks off idle feed hole in body):

        397EC159-38C1-4DB7-9F1A-E405435E53EB.jpeg

        If you look at the previous pic showing the bottom of the carb with no gasket, you can see there is a slight counter bore at the bottom of each barrel.
        The OD of the counterbore is the size of the 1.750 gasket.
        When the 1.750 gasket is used, the idle hole in the body lines up with the gasket, and the baseplate:

        C2E79D66-82A1-407B-8050-E99A52A45C22.jpeg

        I dug thru a bunch of gaskets to see if I had something that had a 1.687 bore, but had the idle feed holes either slotted, or in the 1.750 position...... but I didn’t have anything like that on hand(it may exist and I just don’t have any).
        This carb is getting put back together with the 1.750 gasket(considering the counterbore, this is probably the “correct” gasket for this carb).

        I’m glad I looked!!

        The only reason I can think of for the idle feed hole in the baseplate to be slotted is if perhaps the smaller BG carbs of that era had the idle feed holes in the body located in the normal 1.687 location.
        Then this baseplate would still work.
        As it is, it would work with a Holley/Proform/QFT main body that used a 1-11/16” baseplate.
         
        Last edited: Apr 3, 2020
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        • mderoy340

          mderoy340 Well-Known Member

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          • PRH

            PRH Well-Known Member

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          • Cudafever

            Cudafever Well-Known Member

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            Yes, original main and baseplate for the Demon.

            That was vary good example for that, Thanks PRH

            OK! i wanted to get threw all of this before i asked this next question.

            Does it matter whether.....or which way the main body is installed?
            I know it matter with the Proform because the power valve hole for the secondary is not drilled. But on the demon, its drilled in the main and the baseplate..........so it could be installed either way........right?????????

            I don't know if i put it on backward when i first started having problem with it and pulled it apart. or, if i did it when i just threw the two pieces back together and threw on my shelf or not. BUT the Demon you can tell which way it goes on because it has the bosses cast in to the main body for a vac secondary...............them bosses should be on the passenger side of carb........It was the driver side when i pull the two apart to take pictures.

            IMG_2265.jpg
             
          • PRH

            PRH Well-Known Member

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            As long as the air bleeds were the same front and rear, and you had the metering blocks correct for the front/rear(as the carb was installed on the motor), with that carb...... I don’t see how it would matter.
            You said the baseplate has the hole on the secondary side to provide vacuum to the PV cavity....... but does the secondary side of the main body also have the hole?
            What series of carb is that?
            Mighty Demon?
             
          • Cudafever

            Cudafever Well-Known Member

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            The Proform main body didn't have the hole drilled up into the pv cavity of the secondays. The Demon and the Proform base plate were drilled for both sides. Both only had the PV restrictor in the primary side only.
            No This Demon is not a Vacuum Secondary Carb. It is the "Mighty Demon", Aka Mechanical Secondary Carb.
            Why it has the "provision" to make it a Vac sec carb is crazy to me. The hole is not drilled out or the supports threaded.

            Ok i really felt that it was a non issue, but wanted to see if there was something i was over looking.
             
          • PRH

            PRH Well-Known Member

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            I was referring the hole drilled from the bottom of the main body into the PV cavity.
            Does that main body have that hole drilled into both primary and secondary PV cavities?
            To operate the PV, the hole has to be in the baseplate....... and the main body.

            Hard to really tell from your pic, but it sorta looks like one end is drilled thru...... and the other end isn’t.

            Those holes need to be drilled thru into the PV cavity to allow the PV to operate.

            4D799BD4-D6EB-44BB-94C7-5F01F8FCC1CA.png

            1818601B-16A7-4E82-969B-BE9BE21DB8FB.png
             
            Last edited: Apr 4, 2020
          • Cudafever

            Cudafever Well-Known Member

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            It easy to overlook and even easier to Assume.
            So i had to go back out and pull the base plate back off.
            Yup both holes drilled out on both side.

            Good thought thow.
            If it was only drilled out on one side........It could only go on one direction and work.
             
          • PRH

            PRH Well-Known Member

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            I’m sure within the previous 22 pages of posts it’s already been debated.......

            The way I see it.......if both of those carbs were as sorted out as they could be...... that the PF bodied carb(with its smaller venturi) will end up being the better choice for your application, especially at the elevation you race at.

            After tweaking the calibration, my 850 MD worked pretty well....... but I really only used it on motors making over 600hp.

            I’ll be following along to see how the track comparo between your two carbs plays out.
             
            Last edited: Apr 4, 2020
          • j par

            j par Well-hung Member

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            23 pages on one carburetor!!
            I got 16 pages on two carburetors does that put me in the lead?....lol...
             
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