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Dual carb questions

Discussion in 'The Hokey Ass Message Board' started by colorado51, Jun 27, 2007.

  1. colorado51
    Joined: Feb 24, 2003
    Posts: 1,576

    colorado51
    Member

    Hey all,

    I’m working on a project that I picked up around the first of the year. This is a pretty radical sb chevy with an Edelbrock Pro-Ram intake and two 450 Holley’s (list 9776).

    Kind of a dumb question here, but I thought I’d ask since I’ve never ran a motor with dual carbs before.

    The carbs should be set-up exactly the same, right?:confused:

    The reason why I ask is that I went to re-jet the carbs and I found that the rear carb had 54 main jets and a 2.5 power valve; the front carb had 64 main jets and a 3.5 power valve.

    Thanks

    [​IMG]
     
  2. flathead4d
    Joined: Oct 24, 2005
    Posts: 898

    flathead4d
    Member

    Does it have progressive linkage or straight? That might be the reason for the jet size difference.
     
  3. colorado51
    Joined: Feb 24, 2003
    Posts: 1,576

    colorado51
    Member

    Linkage is straight, (1:1).
     
  4. Petejoe
    Joined: Nov 27, 2002
    Posts: 12,264

    Petejoe
    Member
    from Zoar, Ohio

    Typically on most intake runners setups when the carbs are running straight the jet size and powervalves should be the same.
    A portion of your cylinders could be rich while the others are running lean. Check your plugs and see what effect the differences made on how they're burning.
     

  5. DE SOTO
    Joined: Jan 20, 2006
    Posts: 3,857

    DE SOTO
    Member

    The best i can remember... a 9776 is a 660 center squirt Holly carb.

    They were "THE SHIT" in the '80s meaning EVERYONE who could afford them ran them on there street racers.

    they should be TWINS, all the same internals
     
  6. Petejoe
    Joined: Nov 27, 2002
    Posts: 12,264

    Petejoe
    Member
    from Zoar, Ohio

    Your plugs should tell you which size to use.
    example...
    If you see they are running rich in the back cylinders and fine in the front. Replicate the good carb jet and powervalve sizes in the front.
    Or vice versa..
     
  7. shoprat
    Joined: Dec 23, 2006
    Posts: 1,109

    shoprat
    Member Emeritus
    from Orange, CA

    660's are 4776's. They sure were good. No power valves either.
     
  8. colorado51
    Joined: Feb 24, 2003
    Posts: 1,576

    colorado51
    Member

    Thanks guys.

    The car was running fairly good with the "un-balanced" setup as far as I can tell.

    I went ahead and put 52 main jets and 2.5 power valves in both carbs now, and actually it seems to idle a bit better. Still seemed a little rich though, I think I will go to 50 main jets tonight.

    BTW, this car was running open headers and was from Oklahoma. It now has an exhaust and is at 5000ft elevation, so I am still trying to compensate for those things.:eek:
     
  9. DE SOTO
    Joined: Jan 20, 2006
    Posts: 3,857

    DE SOTO
    Member


    YEAH, THATS THE NUMBER ... BEEN AWHILE SINCE I EVEN THOUGHT ABOUT 4bbl HOLLY'S...

    I STAND CORRECTED ! :D
     
  10. rodknocker
    Joined: Jan 31, 2006
    Posts: 2,265

    rodknocker

    This may sound goofy, but if the car was set up as a drag car,could the carbs be set that way for inertia reasons?I know cars that launch hard have the fuel cells up front for this reason.
     
  11. gasshole
    Joined: Oct 1, 2006
    Posts: 343

    gasshole
    Member
    from new jersey

    I don't think main jets should not come into play at idle unless you have other problems.
     

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