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In need of carb help

Discussion in 'Technical Q&A' started by Dumped308, Jun 25, 2004.

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  1. Dumped308

    Dumped308 Rookie

    Jun 21, 2004
    8
    #1 Dumped308, Jun 25, 2004
    I have a 79 gts and was wondering if any of you out there have a break down of how the carbs go together so i can rejet them and also what jet set up to go with when putting an after market exhaust on my car?

    Nick
     
  2. thecarreaper

    thecarreaper F1 World Champ
    Silver Subscribed

    Sep 30, 2003
    18,067
    Savannah
    #2 thecarreaper, Jun 25, 2004
    find "BIRDMAN" s post on carb tutorial. it has EVERYTHING with pics. i printed the thread its that good.
     
  3. 4re gt4

    4re gt4 Formula 3

    Apr 23, 2002
    2,279
    Roseburg, OR
    Full Name:
    Hans E. Hansen
    #3 4re gt4, Jun 25, 2004
    Pierce Manifolds has a parts diagram on their website.

    However, you don't have to take anything apart to rejet them. Well, OK, you do have to remove the air cleaner, which means the little velocity stacks have to come off. The main/emulsion tube/air corrector assembly comes right out the top, the idles come out the side. Wouldn't hurt to have new O-rings for the idles.
     
  4. Doug

    Doug Formula 3

    Nov 13, 2003
    1,473
    Louisville KY
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    Doug
    #4 Doug, Jun 25, 2004
    Let me know what jets you are interested in. I have extra sets of various sizes. A couple are brand new. I purchased a few sizes to try to find the right configuration. Have a few sets of idles and and extra set of mains. I will sell for 50% of Pierce's price. That is where I purchased them.
    Will check but I think I have:
    135 mains
    40, 50 & 55 idles
     
  5. Dumped308

    Dumped308 Rookie

    Jun 21, 2004
    8
    #5 Dumped308, Jun 25, 2004
    sounds good! What Jet combo did you end up using and what mods do you have? This info should give me an idea of where to start. Your help is ver much appreciated.

    Nick
     
  6. bill308

    bill308 Formula 3
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    May 13, 2001
    1,224
    Windsor, CT
    Full Name:
    Bill Sebestyen
    #6 bill308, Jun 25, 2004
    I believe the 79 cars are fitted with 40DCOE/72/73/74/75 carbs. Stock they are fitted with:

    .55 mm idle jets
    1.25 mm main jets
    2.00 mm air correctors
    F36 emulsion tubes

    To go richer you could try

    .57 or .60 mm idle jets (higher are richer) which affects most of your driving

    1.30, 1.35, 1.40, 1.45, 1.50 main jets (higher are richer) effectively raises the air/fuel curve

    1.90, 2.10, 2.20 air correctors (higher is leaner) effectively changes the slope of the air/fuel curve. Air correctors mainly effect the top end.

    If you don't have to worry about emissions I'd try:

    .60 idle jets
    1.35 main jets

    Then see how that feels.
     
  7. Dumped308

    Dumped308 Rookie

    Jun 21, 2004
    8
    #7 Dumped308, Jun 26, 2004
    Thanks guys
     
  8. f355spider

    f355spider F1 World Champ
    Owner Rossa Subscribed

    May 29, 2001
    18,044
    USA
    #8 f355spider, Jun 26, 2004
    Just as a point of referrence, I had a 78 308 which has the identical stock jetting. The only major mods were cat test pipes, K&N air filter and Crane electronic ignition (oh and NGK platinum EVX plugs). After several dyno runs the tech ended up with 140 main jets, with all the other jets kept the same. Car ran much better, esp. at higher rpms. Though I was running NGK 6 heat range, the plugs seemed to be loading up (fouling some) in city driving, and heat range 5 plugs may have been in order. The car was in an accident, so I was never able to experiment with that.

    135 mains would be a good starting point.

    Dave
     

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