Dismiss Notice

Welcome To CK5!

Registering is free and easy! Hope to see you on the forums soon.

Score a FREE t-shirt and membership sticker when you sign up for a Premium Membership and choose the recurring plan.

Q-Jet re-jet - Dr. Chin?

Discussion in '1969-1972 K5 Blazer | Truck | Suburban' started by ZZ4x4, Oct 22, 2001.

  1. ZZ4x4

    ZZ4x4 1/2 ton status

    Joined:
    Oct 17, 2001
    Posts:
    542
    Likes Received:
    0
    Location:
    Garland, TX
    I've been messing with my Edelbrock square bore to eliminate a flat spot with no success. I am ready to yank that thing off and return to my old trusty Q-jet. Thing is, my new engine has 10:1 compression and a 6000 rpm red-line. I am pretty sure I need to re-jet the Q-jet. I know Steve Chin and others have said they've done this kind of upgrade. I was curious whether anyone has a good place to start for jet size, and part numbers etc... Any other changes needed, like drilling orifices? Looking for max Hp. Thanks, JT
     
  2. Steve_Chin

    Steve_Chin 1/2 ton status

    Joined:
    Mar 6, 2001
    Posts:
    1,126
    Likes Received:
    0
    Location:
    Foster City, CA, USA
    Some of the jetting requirements kind of depend on what series Quadrajet you're running, but I'd start with #74 main jets, #44 primary metering rods, CE secondary rods on a "J" or "K" hanger, and a #922 power piston spring. This is a reasonably good base line for a 350 that makes about 14"-16" Hg vacuum at idle and runs to about 5800 RPM. You'll have to jet up/down and adjust springs and vacuum break orifices in order to get best throttle response and performance.
     
  3. ZZ4x4

    ZZ4x4 1/2 ton status

    Joined:
    Oct 17, 2001
    Posts:
    542
    Likes Received:
    0
    Location:
    Garland, TX
    Thanks Steve. This is just what I was looking for. One more thing....do you know what jets and rods were installed in stock form? It is an original '71 Q-Jet 7041211. Regarding the manifold vacuum, since my HEI advance likes no vacuum at idle, is there a timed port on a q-jet?
    Thanks,
    JT
     
  4. Steve_Chin

    Steve_Chin 1/2 ton status

    Joined:
    Mar 6, 2001
    Posts:
    1,126
    Likes Received:
    0
    Location:
    Foster City, CA, USA
    I haven't got a clue as to what the factory jetting on that carburetor is, sorry.

    Some Quadrajets have ported vacuum sources, some don't. It depends on the original factory setup. Most have the ported source. If it has one, it will be on the driver's side of the front of the carburetor's main body, above the driver's side idle mixture screw, at about the same level as the fuel inlet. I plugged the ported vacuum source off on my Quadrajet because my engine runs a LOT better with full manifold vacuum and a lot of advance coming from the can. You might find that running a limited amount of advance from the vacuum can off of full manifold vacuum works better than having a lot of advance created by manifold vacuum or from ported vacuum. It can't hurt to play with it once you get the carburetor dialed.
     

Share This Page