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A question about q-jets

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by muddin4fun, Apr 5, 2001.

  1. muddin4fun

    muddin4fun 3/4 ton status

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    After seeing how much ya'll like them, I was wondering what does it involve in swaping one onto my '79 350. Isn't there a computer and will I need all the emissions crap on it? I don't know if I'll do it yet, but I was wondering...[​IMG]

    [​IMG]
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  2. dyeager535

    dyeager535 1 ton status Premium Member

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    No computer. If you keep your eyes open, you can pick up Q-jets for $5 a pop, for rebuilders. There is nothing at all difficult about "rebuilding" one, especially since the rebuild kit is basically a gasket kit. Clean out the innards, make sure the primary throttle shaft is still tight (the only thing you might have to pay $40 or so to have done, or $5 to do it yourself)

    Gotta figure out if you want the BOPC style inlet (faces straight forward) or the Chev style (angled to the passenger side) Personally, I like running the steel line, so I use the Chev style on my SBC.

    Depending on the vintage carb you get, you may end up plugging/capping a few vacuum ports.

    Dorian
    My K5 and Chev/Olds tech/links page: <A target="_blank" HREF=http://www.dorianyeager.com/index2.html>http://www.dorianyeager.com/index2.html</A>
     
  3. muddin4fun

    muddin4fun 3/4 ton status

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    So, what makes them so unadjustable? Do they just run off vacum so to speak? I've never seen one in person is why I have all the stupid questions, LOL!

    [​IMG]
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  4. Depdog

    Depdog 1/2 ton status Author

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    They are not unadjustable, you just have to know how to adjust them. Grim is the Carb King as far as the Q jet is concerned, at least amoung the folks I know.

    Depdog

    <font color=blue>Weenie K5, little mods' Small Tires!</font color=blue>

    <A target="_blank" HREF=http://depdogsk5.coloradok5.com>http://depdogsk5.coloradok5.com</A>
     
  5. dyeager535

    dyeager535 1 ton status Premium Member

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    They run off of vacuum, essentially. There are other factors involved of course, but vacuum is mainly it. They ARE adjustable, but never having dealt with any other carb, I wouldn't know how they stack up on adjustability. One thing I do know is that you set a Q-jet up right and forget about it. 100,000 miles later, clean it up again, and good to go.

    The important stuff, choke, mix, idle speed, secondary rods/hangar, is all easily accessible, so other than that, you just have to set the float. You can check out the links on my page below for some Q-jet info, including ID and some tuning tips.

    Dorian
    My K5 and Chev/Olds tech/links page: <A target="_blank" HREF=http://www.dorianyeager.com/index2.html>http://www.dorianyeager.com/index2.html</A>
     
  6. muddin4fun

    muddin4fun 3/4 ton status

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    I read your carb shoot out thing. It's got me thinking. Do the q-jets really feel less powerful or is it just cause of the "finesse" they bring? I've got a 600cfm on mine and it looks like the smallest q-jet is 750. How would that not be as powerful?

    [​IMG]
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  7. tRustyK5

    tRustyK5 Big meanie Staff Member Super Moderator GMOTM Winner Author

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    I have had the Q-jet on my Jimmy as well as a vacuum secondary Holley 600, and lastly an Edelbrock electric choke 600.
    Pro's and cons of each from a first hand point of view.

    Q-jet decent performance, sort of. Good mileage. I had a lot of trouble trying to get it set up right, although in its defense the throttle shaft may have needed re-bushing.

    Holley...better throttle response, really shined at the top end (where I didn't need it) ate more gas and would never start when hot. Would not stay in 'tune'. I was re-tuning that thing once a week. My first and last holley

    Edelbrock...I bought it brand new. Ran extremely well right out of the box. Very simple to adjust. By far the most crisp off idle response of the three. Best overall performance although the Holley had it beat at the upper end of things. Similar mileage to the Q-jet. The only con is operating at extreme angles, I have had it start to run bad and flood on a bad angle, but I haven't installed the spring loaded needle and seat yet.

    Quite honestly if I make another change it will be to FI, I'm pretty happy with my Edelbrock but a carb just seems like a band-aid compared to FI.

    Rene

    [​IMG]<A target="_blank" HREF=http://jules.coloradok5.com>http://jules.coloradok5.com</A>
     
  8. dyeager535

    dyeager535 1 ton status Premium Member

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    Straight out of the box, NO carb is going to be optimized for use on every engine. The square bore carbs have bigger primaries (typically) than the Q-jet, as well as same size secondaries. Tuned correctly, I think the Q-jet is capable of performing just as well as any other comparable carb. Granted, I think for racing applications, you'd have to spend a lot more time on the Q-jet than say a Holley, but the Q-jet was designed as a compromise from teh start (performance and economy) so to expect it to perform as well as any race carb just isn't fair.

    The Qjet, due to its design, will only flow what your engine demands, again, basically. Most engines don't NEED 750 CFM, so the 750 can be overkill, but its there if you do need it. The Q-jet has tiny primaries (smaller than even a 600 square bore) so the economy comes from this. The secondary bores are enormous, and thats where the power comes from.

    On a square bore carb, the bores are the same size, primary/secondary.

    Dorian
    My K5 and Chev/Olds tech/links page: <A target="_blank" HREF=http://www.dorianyeager.com/index2.html>http://www.dorianyeager.com/index2.html</A>
     
  9. tRustyK5

    tRustyK5 Big meanie Staff Member Super Moderator GMOTM Winner Author

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    What I meant by "Running extremely well right out of the box" was that I didn't have to make any jetting changes, or play with the metering rods...all I had to adjust was the mixture and idle speed.

    I am one of the few (it seems) that just don't like or have never had a good experience with a Q-jet...but then I've only had about 20 of them on different cars so my experience might be a little limited...[​IMG]

    Rene

    [​IMG]<A target="_blank" HREF=http://jules.coloradok5.com>http://jules.coloradok5.com</A>
     
  10. muddin4fun

    muddin4fun 3/4 ton status

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    Does anyone know how good the off-road needles for the edelbrock performer are? They say it makes it as good as a q-jet on angles.

    [​IMG]
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  11. Emmettology 101

    Emmettology 101 3/4 ton status

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    My one friend is running this set-up with his JE*P... He ran without the offroad kit and it bogged n almost any angle. Then with the offroad kit it helped but I dont htink it is still as good as a Q-Jet!


    <font color=green><A target="_blank" HREF=http://emmett.coloradok5.com>http://emmett.coloradok5.com</A></font color=green>[​IMG]
     
  12. muddin4fun

    muddin4fun 3/4 ton status

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    Well, I would expect that cause aren't the fuel bowls in a different location? I don't know....my hubby doesn't like q-jets and doesn't like to try new things (he doesn't have any experiance with them also [​IMG]) so I'm trying to get a solid argument. I sure don't want the truck dieing on an angle when I need it to be running!!!

    [​IMG]
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  13. dyeager535

    dyeager535 1 ton status Premium Member

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    Not sure exactly the float situation on the E-brock, but I know some of the aftermarket carbs have less than optimally designed floats and floatbowls for certain conditions. The Q-jet float should excel at sidehilling, and probably almost as good nose or tail up in the air. The carbs that have floats mounted "sideways" like most FWD engines are mounted "sideways", would have more of a problem sidehilling than the "straight back" style float that the Q-jet has.

    There would be no way to cure it totally besides redesigning the float and bowl area.

    Dorian
    My K5 and Chev/Olds tech/links page: <A target="_blank" HREF=http://www.dorianyeager.com/index2.html>http://www.dorianyeager.com/index2.html</A>
     
  14. muddin4fun

    muddin4fun 3/4 ton status

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    That's it!!!!!! I'm designing my own carb!!!!!!!! Check back with me in a few years!! LOL!

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  15. Grim-Reaper

    Grim-Reaper 3/4 ton status Author

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    Muddin what's on your truck now? It came with a Quad.

    Diging it in the dirt with my K5's
    Grim-Reaper
    <A target="_blank" HREF=http://grimsk5s.coloradok5.com/>http://grimsk5s.coloradok5.com/</A>
     
  16. muddin4fun

    muddin4fun 3/4 ton status

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    It looked like a Holley. Right now it's got an Edelbrock Performer 600cfm. I think I'm gonna put the offroad needles and such on it ($12) and see what that does and then decide.

    [​IMG]
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  17. slider79blazer

    slider79blazer 1/2 ton status

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    the floats on a Q-jet are in the middle of the bowl thats why
    they don't stall or bog down on angles. my 79 has a Q-jet on
    it and it has never missed a beat.my buddies j*ep has a holley
    and it dies all the time going uphill.

    whats a 4 letter word for farm wagon? (ford)
     
  18. Twiz

    Twiz 1/2 ton status

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    I've been on hills I couldn't walk, and the q-jet was runin' fine (sort-of)

    Twiztid
     
  19. Sparky

    Sparky 1/2 ton status

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    My q jet (after i rebuilt it) has been a dream come true. Never dies on angles. Gets the same gas mileage no matter how easy or soft I drive it. Starts up evry time with no porblems. I dont have to worry about any electric parts breaking. The only time it ever skips a beat is if I drive fast over some heavy bumps. I think it causes the float bowl to drain or something, but as soon as I get back on a smooth surface or slow down its fine. This only happened a couple of times. Once I was trying to beat a red light and went too fast over an intersection. Pretty much jumped the truck. The other time I was racing a friend back to my house and I took a off road short cut. I was driveing too fast over the ruff stuff and stalled for a second, but caught back on in no time.

    Sparky

    When all else fails... Check the blinker fluid.
    78 K-5
     
  20. Burt4x4

    Burt4x4 3/4 ton status

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    Hey Sparky, just an FYI if you put a 3" piece of fule line on the float bowl vent tube(located on the top front of the carb) this will cure your bummpy sindrome for life!! Prevents the fule from sloshing into the primaries! Tryit you'll like it!!

    72K5[​IMG]Led Zeppelin[​IMG]Rock ON![​IMG]
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