Hey Quadrajet people
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500, 472, 425, 368 Discussion, Hey Quadrajet people in Cadillac Engine Technical Discussion; I was just wondering how some of you have your quadrajets set up. I have a 76 500 with 76 ...
  1. #1
    cadder2000 is offline Cadillac Owners Member
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    Hey Quadrajet people

    I was just wondering how some of you have your quadrajets set up. I have a 76 500 with 76 q-jet. stock setup calls for .070 primary jets .039 primary rods, and DH secondary rods. I had the thing rebuilt awhile back and the guy at the carb shop said that the primary rods that were in it were 40Ls. Since then I have messed around with the primary jetting and have gone from 70s to 74s. Right now I am running 72 primarys. The throttle response with 70s was much better but the top end seems to suffer, kind of goes flat around 3500 rpm. My thoughts were to move to fatter rods while moving up in the primary size also. I think this should give crisp throttle response while keeping cruise metering the same and giving me more power at WOT. Don't know if I should mess with secondary rods. I haven't messed much with q-jets much until now but thought I would give them a chance. I'm trying to balance decent gas mileage during cruise, but having power available when I want it. My engine upgrades are : around 9.2-9.5 compression, modified intake with carb spacer,MTS #10 cam, 2.5 in dual exhaust. Let me know what you Q-jet fans are running. Thanks

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  3. #2
    BluEyes's Avatar
    BluEyes is offline Cadillac Owners Enthusiast
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    Re: Hey Quadrajet people

    There is an excellent article out there on Q-jet tuning by a guy named Lars Grimsrud. Goggle that, it's long, but throughly goes through the tuning procedure for a Q-jet. Very different from what tuning a Holley would be.
    Honestly, if your engine is still stock, I'd go back to that and start there (also Lars' advice). GM spent alot of time tuning these carbs at the factory.
    Oh, as for your bog, that might be the secondary air door, or the vacuum can. Google Q-jet and Damon. He has a number of great tips on his site. No sense in me typing a bunch when he already has.

  4. #3
    cadder2000 is offline Cadillac Owners Member
    Automobile(s): 1982 fleetwood w/ 500cid, 1990 Brougham 'D Elegance 5.7
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    Re: Hey Quadrajet people

    Thanks for the good info

  5. #4
    creeker is offline Cadillac Owners Connoisseur
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    Re: Hey Quadrajet people

    I looked up that lars grimsrud website, it's great , lots of info. tnx.

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