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Carb Jets

Discussion in '40- & 55-Series Tech' started by drohweder, Nov 19, 2003.

  1. drohweder

    drohweder

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    So I am rebuilding my Rochester Quadrajet and am wondering what jets to go with. I have no experience with these things and was wondering if there is a specific jet that works well. I am in Suisun,CA so my elevation is abut sea level but I do run up to Tahoe during the winter and summer months. On the dyno my untuned carb was running lean. Your thoughts? Carb #89058 2293W Thanks!
     
  2. drohweder

    drohweder

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    Upon more research it looks like there is a 1902 stamped on the carb as well. I think the first number is the serial number.
     
  3. Rice

    Rice SILVER Star

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    Dan,
    You put your 55 on a chassis dyno, right? What was used to determine your carb was running lean? Were there sensors being used to monitor exhaust gas temperatures?

    Unless there were some significant change in either engine configuration or altitude I would suggest sticking with original jets. If original equipment on the engine was that carb it would already have been calibrated for jet size. To find out if the engine is presently running lean or rich your best indicator is reading the spark plugs. Trips to higher altitudes will cause the engine to run a little rich (and therefore a small loss in power), however will not damage an engine the way a lean setup can.
     
  4. theo

    theo

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    1902 is an Edelbrock number.

    From the Edelbrock website:
    "Q-Jet Series Carburetor - 4MV - 1974-78
    For 1974-78 350-454 Chevy/GMC trucks and cars with a divorced style choke. Compatible with EGR. Main Jet: .069; Metering Rods: Primary-36B, Secondary-DR.
    750 cfm with divorced choke #1902"

    These specs are probably good for you since I think sea level is the level by which all levels are leveled.. :)

    Remember that jetting a carb means matching not just the mains, but the metering rods and springs too.

    If you want to get into it I have a couple of papers I "harvested" off the web that explain how to tune a quadrajet. But you could just put a kit in it using stock jetting and probably be fine.
     
  5. drohweder

    drohweder

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    Rice:
    When I dyno'd the pig it was hooked up to a computer connected by a wire to one of the spark plug wires and a fuel-air measureing system inserted in the tail pipe. The place that did it does a lot of work for some of the cars racing at Infineon so I would assume it was set up properly.

    theo: thanks for the specs. I also checked out the edelbrock site and came up with those numbers but I was getting confused talking to the guy at the local autoparts store so I ended up calling Edelbrock and talking to tech support. They said the 1902 is the only carb with a divorced choke and the Rebuild kit (#1920) is $44. Sometimes these things are confusing first time around.

    So what comes in a rebuild kit and what additional parts might I need to replace or update. Will a new accelerator pump add anything? How often does the fuel filter need to be replaced? What power piston spring strength is indicated.

    Thanks for your help, my father in law was a mechanic for years and wants to tune the carb while he is out for Thanksgiving so I need to make sure I have all the parts needed so we can do it. See one,do one, teach one has always been a good motto :D

    ???Sorry for all the questions hope you don't feel like :slap: ...ing me around!
     
  6. Isotel

    Isotel

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    While on the Subject, Any Colorado or, High altitude guys running Q-jets on their rigs.. i am about to rebuild the carb and i want it to preform good around 6,000 feet, (where i live) all the way up to 14,000(where i may be going), and do best at like 8,000-10,000(where i will do alot of wheeling)..
     
  7. theo

    theo

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    drohweder (what kind of name is that? :D)

    The kit comes with a new accelerator pump, along with gaskets (of course), needle and seat, pump discharge ball (just a ball bearing), and maybe a couple of other small parts.

    $44 seems high but maybe not.

    I would use stock metering rod springs at first (Reuse the ones in it if the kit doesn't have them. I can't remember if it does.) Changing springs gives subtle changes in the transition from idle to part throttle and depends on manifold vacuum. So each engine behaves differently. If you get to the point where you think you're bogging a little on take-off because it's lean you could try heavier springs to lift the rods a little sooner. If it seems a little rich on take-off then lighter springs could help. But that's after you think you have the best main jet/metering rod combo in place.

    And no amount of spring changes will fix a larger problem from vacuum leaks or clogged passages or whatever. Those are the more common problems with quadrajets.

    Hope this helps.
     
  8. drohweder

    drohweder

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    Dan Rohweder....see where the name comes from? Could be Dr. Ohweder but its not. Should have thought about my name a bit more before setting up my profile. I could have been so much cooler...but Its just a name. Perhaps a redefineing moment is in order:)

    Where the hell are you going to drive your cruiser to 14K? I grew up wheeling in colorado and the highest I ever got was about 13.2K. Let me know what trail it is because telling people I did a 14er is cool and its alot easier in a truck than by foot!!

    Thanks theo for the tips!