Those with Street Demon Carburetors....

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

  1. RustyRatRod

    RustyRatRod Just another dumbass. Technical Editor

    Messages:
    46,175
    Likes Received:
    10533
    Joined:
    Jun 7, 2010
    Location:
    Georgia
    View My Photos
    Local Time:
    1:19 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
    • Agree Agree x 1
    • 1994redram

      1994redram FABO Gold Member FABO Gold Member

      Messages:
      836
      Likes Received:
      347
      Joined:
      May 9, 2012
      Location:
      Oklahoma
      Local Time:
      12:19 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.
       
      • Like Like x 1
      • jos51700

        jos51700 Well-Known Member

        Messages:
        4,281
        Likes Received:
        1028
        Joined:
        May 24, 2009
        Location:
        Bel-Ray
        Local Time:
        12:19 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. Technical Editor

        Messages:
        46,175
        Likes Received:
        10533
        Joined:
        Jun 7, 2010
        Location:
        Georgia
        View My Photos
        Local Time:
        1:19 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.
         
        • Like Like x 1
        • dustadude

          dustadude Well-Known Member

          Messages:
          169
          Likes Received:
          12
          Joined:
          Jan 30, 2014
          Location:
          San Lorenzo, Ca (SF East)
          Local Time:
          10:19 PM
          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:
          14,118
          Likes Received:
          3557
          Joined:
          Jan 19, 2014
          Location:
          South-Central Manitoba,Canada, 900ftelevation
          View My Photos
          Local Time:
          12:19 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:
          31,706
          Likes Received:
          10042
          Joined:
          May 21, 2011
          Location:
          Arroyo grande ca
          Local Time:
          10:19 PM
          Stock converter, RRR ?..
          These carbs, are intriguing me....
           
        • Abodybomber

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

          Messages:
          31,706
          Likes Received:
          10042
          Joined:
          May 21, 2011
          Location:
          Arroyo grande ca
          Local Time:
          10:19 PM
          625 size..?:)
           
        • 12many

          12many Well-Known Member

          Messages:
          462
          Likes Received:
          527
          Joined:
          Dec 14, 2016
          Location:
          South Carolina
          Local Time:
          12:19 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. Technical Editor

          Messages:
          46,175
          Likes Received:
          10533
          Joined:
          Jun 7, 2010
          Location:
          Georgia
          View My Photos
          Local Time:
          1:19 AM
          My truck has the infinitely adjustable converter. A clutch. lol
           
          • Like Like x 1
          • RustyRatRod

            RustyRatRod Just another dumbass. Technical Editor

            Messages:
            46,175
            Likes Received:
            10533
            Joined:
            Jun 7, 2010
            Location:
            Georgia
            View My Photos
            Local Time:
            1:19 AM
            Yes sir.
             
          • DFX 340 Duster

            DFX 340 Duster FABO Gold Member FABO Gold Member

            Messages:
            1,577
            Likes Received:
            331
            Joined:
            May 14, 2009
            Location:
            Orange County CA
            Local Time:
            10:19 PM
            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:
            746
            Likes Received:
            78
            Joined:
            Feb 15, 2011
            Location:
            south shore, N.S.
            Local Time:
            2:19 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:
            462
            Likes Received:
            527
            Joined:
            Dec 14, 2016
            Location:
            South Carolina
            Local Time:
            12:19 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:
              3,283
              Likes Received:
              302
              Joined:
              Jan 4, 2008
              Location:
              Fort Collins, CO
              View My Photos
              Local Time:
              11:19 PM
              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:
              3,912
              Likes Received:
              695
              Joined:
              Nov 2, 2010
              Location:
              p. e. i.
              View My Photos
              Local Time:
              2:19 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:
                484
                Likes Received:
                102
                Joined:
                Apr 12, 2015
                Location:
                Amelia Oh
                Local Time:
                1:19 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:
                  7,362
                  Likes Received:
                  1298
                  Joined:
                  Oct 27, 2010
                  Location:
                  WV
                  Local Time:
                  1:19 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
                  • Cuprum-74

                    Cuprum-74 Moparus Fanaticus

                    Messages:
                    467
                    Likes Received:
                    43
                    Joined:
                    Dec 6, 2012
                    Location:
                    Utah
                    Local Time:
                    11:19 PM
                    I have been running the Street Demon 750 in mine for almost a year now. I love this thing, its like an offspring between a Thermoquad and an AVS.
                    I had to lean the primaries out quite a bit with rods + jets. (I live at 4500 feet above sea level).
                    I drove to Louisville, CO and back (506 miles one way) a few weeks ago.
                    No issues! (other than the alternator going out in a blaze of glory and frying the fusible link plus voltage regulator)
                    Mileage was 14.3 mpg driving though a 45-50 mph varying crosswind/headwind to about 16 mpg's on flat areas. The best was 17.4 but was a lot of downhill.
                    This was maintaining between 70-72 mph's which is about 3,000 rpms. Except for construction and other areas that had 60-65 mph speed zones.
                    I have 3.21 rear gears and 245/60R15 tires. (26.5in diameter)
                    There is one thing that would've made this trip a little better... A/C! Which is next on the list, I'll have to boost up the charging system to more than what it is now at 65 amps.
                     
                    • Like Like x 2
                    • RustyRatRod

                      RustyRatRod Just another dumbass. Technical Editor

                      Messages:
                      46,175
                      Likes Received:
                      10533
                      Joined:
                      Jun 7, 2010
                      Location:
                      Georgia
                      View My Photos
                      Local Time:
                      1:19 AM
                      No. Since that's adjustable, that would have no bearing. I am talking about the throttle blade travel. Not the air door.
                       
                      • Thanks! Thanks! x 1