Those with Street Demon Carburetors....

Discussion in 'Fuel and Air Systems' started by RustyRatRod, May 29, 2018.

  1. RustyRatRod

    RustyRatRod Just another dumbass. FABO Gold Member Technical Editor

    Messages:
    45,258
    Likes Received:
    9122
    Joined:
    Jun 7, 2010
    Location:
    Georgia
    View My Photos
    Local Time:
    8:26 AM
    I just put a used 625 Street Demon on my 75 F250. 351M, Weiand Action plus, GM style HEI 20* initial and 35 total in by 3000. Exhaust manifolds. I THINK it MIGHT have the Melling, TRW, Elgin, "everybodys" grind that's like 204/214 @ .050, but on a Ford the lift is more because of the 1.73 rocker ratio. .484 and .512.

    Anyway, I got the carb in a trade. It needed some repairs. The secondary air door spring was broken. Thermoquad air door spring fits perfectly. Put a kit in it. Cleaned it all up lookin like new.

    This thing runs like a bat out of hell now. When that secondary door opens, this big old truck moves. Anyway, I am noticing something a little different from other carburetors and wondered if others running these noticed it too.

    There's "not a lot" of the primaries. In other words, the primaries have a kinda short travel. The secondaries come in pretty quick with the pedal travel. I kinda like it. Anybody else notice it?
     
    • Like Like x 1
    • 1994redram

      1994redram FABO Gold Member FABO Gold Member

      Messages:
      673
      Likes Received:
      202
      Joined:
      May 9, 2012
      Location:
      Oklahoma
      Local Time:
      7:26 AM
      I have and I LIKE it. Motor goes from mild to wild when the secondaries open. Sounds awesome. I love my street demon carb. I'm planning on getting the larger one to replace my 625 and hopefully free up some power.
       
    • jos51700

      jos51700 Well-Known Member

      Messages:
      3,913
      Likes Received:
      791
      Joined:
      May 24, 2009
      Location:
      Bel-Ray
      Local Time:
      7:26 AM
      Sounds about like the old smallblock TQ on a 318 with a midrange cam. The primary's are pretty tame, and the secondary's....aren't.
       
    • RustyRatRod

      RustyRatRod Just another dumbass. FABO Gold Member Technical Editor

      Messages:
      45,258
      Likes Received:
      9122
      Joined:
      Jun 7, 2010
      Location:
      Georgia
      View My Photos
      Local Time:
      8:26 AM
      I'll have to get Kitty to work the video camera so yall can see how effective this thing is. It's a 75 F250, do it's NOT light, but it slap gets up now.
       
    • dustadude

      dustadude Well-Known Member

      Messages:
      158
      Likes Received:
      9
      Joined:
      Jan 30, 2014
      Location:
      San Lorenzo, Ca (SF East)
      Local Time:
      5:26 AM
      Just like the old tq, secondaries open up and your butt goes back into the seat
       
    • AJ/FormS

      AJ/FormS 367 FormS clone 3.09-1.92-1.40-1.09-.78od 3.55s

      Messages:
      12,764
      Likes Received:
      2740
      Joined:
      Jan 19, 2014
      Location:
      Southern Manitoba,Canada, 900ftelevation
      View My Photos
      Local Time:
      7:26 AM
      Kindof like the TB in my 92 Explorer was. The first 30% of the pedal travel opened her up probably over 50%, and bam! she jumped off the line. But there wasn't much left from there to full pedal travel.
      My wife's Honda Pilot is like that too, and in addition it has a fairly low first gear.I have to be careful not to give my Honey whiplash .
       
    • Abodybomber

      Abodybomber Breaking street machines , since 1983.....:)

      Messages:
      30,560
      Likes Received:
      8977
      Joined:
      May 21, 2011
      Location:
      Arroyo grande ca
      Local Time:
      5:26 AM
      Stock converter, RRR ?..
      These carbs, are intriguing me....
       
    • Abodybomber

      Abodybomber Breaking street machines , since 1983.....:)

      Messages:
      30,560
      Likes Received:
      8977
      Joined:
      May 21, 2011
      Location:
      Arroyo grande ca
      Local Time:
      5:26 AM
      625 size..?:)
       
    • 12many

      12many Well-Known Member

      Messages:
      401
      Likes Received:
      446
      Joined:
      Dec 14, 2016
      Location:
      South Carolina
      Local Time:
      7:26 AM
      I've been doing a lot of fine tuning on the 750 version. OOTB (for my setup) the primaries were way rich. I actually had to use the smaller primary jets from the 625 jet kit (for my son's car) along with metering rods from the 750 kit in order to get it right. Theses carbs respond to the most incremental changes quite noticably. Only negative I've come across was on the son's 625, the choke plate hung up, actually hyper extended (where it closed and the rear of the plate came out of the opening and hung-up) On the 750 the Ford kickdown arm was hanging up on bigger throttle openings and the throttle then stuck open. I hacked it off and no issues since. Nice carbs, but they can suffer from some niggles that shouldn't occur.Heres a nice article on the carbs, and some tuning advice:. www.chevyhardcore.com/tech-stories/tech-tuning-tips-to-get-the-most-out-of-the-street-demon-carburetor
       
    • RustyRatRod

      RustyRatRod Just another dumbass. FABO Gold Member Technical Editor

      Messages:
      45,258
      Likes Received:
      9122
      Joined:
      Jun 7, 2010
      Location:
      Georgia
      View My Photos
      Local Time:
      8:26 AM
      My truck has the infinitely adjustable converter. A clutch. lol
       
    • RustyRatRod

      RustyRatRod Just another dumbass. FABO Gold Member Technical Editor

      Messages:
      45,258
      Likes Received:
      9122
      Joined:
      Jun 7, 2010
      Location:
      Georgia
      View My Photos
      Local Time:
      8:26 AM
      Yes sir.
       
    • DFX 340 Duster

      DFX 340 Duster FABO Gold Member FABO Gold Member

      Messages:
      1,567
      Likes Received:
      316
      Joined:
      May 14, 2009
      Location:
      Orange County CA
      Local Time:
      5:26 AM
      Rusty, do you think there is a difference in spring rates between the Demon secondary air door spring and the TQ one? Maybe that would account for the short pedal before the secondaries open?
       
    • lil red

      lil red Well-Known Member

      Messages:
      740
      Likes Received:
      70
      Joined:
      Feb 15, 2011
      Location:
      south shore, N.S.
      Local Time:
      9:26 AM
      got a 750street demon to replace a 670 holley that replaced my od TQ. Love the demon, responsive like the TQ. I have the same issue with the choke plate, I was going to drill/tap the tower to put in a set screw to act as a stop. The only thing i did was tune the air door.

      having some issues with the choke nadjustment, idles well for a few seconds, then runs rich so i have to kick the choke off
       
    • 12many

      12many Well-Known Member

      Messages:
      401
      Likes Received:
      446
      Joined:
      Dec 14, 2016
      Location:
      South Carolina
      Local Time:
      7:26 AM
      Simple fix, place a flat washer under the lock nut for the stud. The washer hangs over enough that the choke plate hits it, choke plate not going any further yet it closes as it should when cold.:thumbsup:
       
      • Like Like x 1
      • Thanks! Thanks! x 1
      • MOPEkidD-3

        MOPEkidD-3 Torsional Member

        Messages:
        3,209
        Likes Received:
        235
        Joined:
        Jan 4, 2008
        Location:
        Fort Collins, CO
        View My Photos
        Local Time:
        6:26 AM
        I have the 750 version which was last running on a mild built 360, I didn't notice the primaries having short travel since the difference in airflow of the bigger one comes solely from bigger primaries, so I didn't need to give it much throttle to get going. I believe the linkage arm that opens the secondary throttle plate is adjustable, have you tried that?
         
      • jimjimjimmy

        jimjimjimmy lobsterman FABO Gold Member

        Messages:
        3,766
        Likes Received:
        598
        Joined:
        Nov 2, 2010
        Location:
        p. e. i.
        View My Photos
        Local Time:
        9:26 AM


        if I understand your question right I would say no the spring rate is adjustable and a very important in tuning .
         
        • Thanks! Thanks! x 1
        • Agree Agree x 1
        • mario03srt

          mario03srt FABO Gold Member FABO Gold Member

          Messages:
          459
          Likes Received:
          95
          Joined:
          Apr 12, 2015
          Location:
          Amelia Oh
          Local Time:
          8:26 AM
          I LOVE Adrianne Boob-Beau!!!! One hot mama from the 70/80's!

          Now back to our regular programming!

          Marion
           
          • Agree Agree x 1
          • sireland67

            sireland67 Well-Known Member

            Messages:
            6,888
            Likes Received:
            947
            Joined:
            Oct 27, 2010
            Location:
            WV
            Local Time:
            8:26 AM
            I have had one since they first come out, it is really a set it and forget it carb, way better than than anything else for driving everyday.
            I get 14.5 mpg out of my old 4x4 truck every tank with this carb.
             
            • Like Like x 1