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Carb Jets (Q-jet)

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by Corey 78K5, May 27, 2002.

  1. Corey 78K5

    Corey 78K5 1 ton status

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    I'm rebuilding a 650 cfm Q-jet and was wondering what size jets are best for a 350 with a standard bore performer intake and headers also a RV cam?
     
  2. Zeus33rd

    Zeus33rd Smarter than you GMOTM Winner

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    Hmmm.....No such thing as a 650cfm q-jet. Just 750 & 800. As for your question...lol, I have no idea. /forums/images/icons/smile.gif
     
  3. Corey 78K5

    Corey 78K5 1 ton status

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    No kidding /forums/images/icons/blush.gif I thought thats what a 350 used. Of corse Im no expert on carbs but it's still news to me I did look on a couple other sites and all I found was 750 795 800 and 850 so you may be right. Can any one else confrim this.
     
  4. Triaged

    Triaged 1/2 ton status

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    Q-Jets came in 750 or 795(which most people call the 800). The 850 is a ededlbrock performer q-jet that never came from the factory.
     
  5. Blazer79

    Blazer79 1/2 ton status

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  6. Corey 78K5

    Corey 78K5 1 ton status

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    My Bad! I guess thats why we have the forums here to learn stuff like this. So we go back to the original question but with the 750 cfm /forums/images/icons/wink.gif
     
  7. Corey 78K5

    Corey 78K5 1 ton status

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    Hey Juan I dont have a pic and I wont get my cam back for another week or two But I do have the model # 7045583 its off of a 75 Chevy truck with a 350 and California emmisionsoh and a manual tranny. I just assumend thats what size it was I just never read or had been told diffrent oh well.
     
  8. Jay73K20

    Jay73K20 Registered Member

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    Yes the Q-jet cam in two different sizes, 750 and 800 (795). But the factory limited the cfm by stops grooved into the secondary top shaft. So if the top butterflies don't open up completely vertical then your carb won't flow the complete 750/795 cfm
     
  9. dyeager535

    dyeager535 1 ton status Premium Member

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    Not sure about which jets/rods would be best (its not one size fits all 350's, so its some testing) , but are you talking on the primary side or secondary?
     
  10. Blazer79

    Blazer79 1/2 ton status

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    Well, my Edelbrock Q-jet and the Rochester Q-jet I had before had 0.069" main jets. It was running too rich for my 4000 ft. altitude. I went with 0.068" on the Edelbrock and it's fine now. I'm using Edelbrock main jets, but I believe they are interchangeable with the Rochester ones.

    Hope this helps.

    PD: My Rochester was 795cfm, and the Edelbrock is a 750 (model #1902)

    Good luck.
     
  11. 91K5

    91K5 1/2 ton status

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    The best way to jet a Quadrajet is to run it on the motor and go from there. If you have a vacuum gauge, connect it to the manifold vacuum port and adjust the idle mixture screws until you get the highest possible vacuum. Then go drive it on the highway and get on it a bit, dont let it idle as much as possible. Then bring it home and let it cool down and pull some plugs and check them for color, you want a tan color around the electrode. If the plugs are white you want to richen it up with larger jets, if they're black/wet you want to use smaller jets. The Quadrajets are a very forgiving carb with the air-valve design adjusting the mixture by themselves to an extent, and a lot of times re-jetting isnt required unless you have some modifications that require it. Hope this helps.
     
  12. Corey 78K5

    Corey 78K5 1 ton status

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  13. Ben Malinski

    Ben Malinski Guest

    Re: Question for 91K5

    Manifold vacuum port? Explain please its exact location. I'm new to these Q-jets.
    Right now the only hoses I have connected to the carb is the distributor hose and where it should be connected to is still a mystery! Some say connect it to the passenger side front corner of the carb some say connect it to the drivers side. I have connected the hose to both locations and notice no difference in performance. The other line is for the brake booster. But, when using a vacuum guage to adjust the air/fuel mixture, where do I connect it to? I have no EGR and NO smog items on this truck. Lucky to live overseas! Thanks!
     
  14. dyeager535

    dyeager535 1 ton status Premium Member

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    Sorry my sites not up, it has a bunch (all?) of the primary rods/jets listed on it. can't remember where i got the list from, but wherever it was, its likely still able to be found via yahoo seatch etc. (I swear I'll mirror it later, too much traffic on mine amazingly)

    Anyways, how I did mine, whether wrong or right, is start with good ignition (plugs, wires, cap/rotor in good shape) and with whatever the carb had in it for rods/jets. I leaned out the primary mix by going with thicker and thicker rods, (what I had on hand) until it started to "surge" at cruise, 35MPH or so on flat ground. I went back one "step" richer, and left it at that. Still running a bit lean, plugs come out pretty white, and a little eroded for their age (but they are $.99 autolites, that may be the erosion cause lol) but I average 13city 18 freeway so I don't think I did too bad.

    To be honest, I should have messed around with power piston springs and perhaps jets too, but I didn't have a large selection of either, and no way to measure spring "rates" so i didn't mess with them...they may have helped to, had I spent the time or had the parts.


    Acceleration is great, and since the primaries are a relatively small part of WOT, really don't hurt to be as lean as possible as long as it still runs well.
     
  15. Blazer_Boy

    Blazer_Boy 1/2 ton status

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    Well I know I'm a few weeks behind but I was poking around on stuff to set idle mixtures and found this. I had a hand full of jets and rods laying around and threw together something pretty hot this morning. I stole the recipe from the Edelbrock #1904 M4ME Q-Jet. I was just lucky enough to have the exact same parts! Jets.... 73s Primary Rods... 50M Secondary Rods... DR Hanger... ? I just used a "K" because I've heard it mentioned quite a few times. Leave the power piston alone because it sounds like you will be pulling near stock vacuum with an RV cam. If you feel you are in the power circuit too much, use a weaker spring. If you want more, use a heavier springs. Too much or too little can produce a bog or hesitation. What altitude are you at?
     

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