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Quadrajet or something else???

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by Sparky, Nov 6, 2000.

  1. Sparky

    Sparky 1/2 ton status

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    I have a 78 with a 350/350/np203. My question involves carbs. Currently I am provideing my engine gas through a quadrajet. From what I have heard and expericenced they are great carbs just extremely difficult to tune and deal with. The problem I have now is that my Blazer runs like crap when it is cold. It hesitates and bogs down severely when I aply the gas. Once it wams up it is fine. The other problem is that it runs too rich, and wont lean out. I could turn the needles all week and notice hardly any difference. What do you all suggest I do? My options are... 1. Rebuild the Quadrajet. or 2. buy a new carb.

    What are the advantages and disadvantages of the differnt carbs out there? If I do decide to rebuild mine how certain can I be that I can get it to run right. I have decent experience and have rebuilt a few other carbs with success, but from what I hear the Quadrajet is pretty tricky. I would like the best gas mileage I can get without suffering any performance fall from where I am now. Let me know your suggestions.

    Thanks again,

    Sparky

    78 K-5
     
  2. Blazer79

    Blazer79 1/2 ton status

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    If you get a new one, I'd recommend a new Edelbrock Quadrajet. The reason I changed my old one was exactly the same as yours. Had to crank for about 5 minutes before it started. When it finally did, it was the worst idle you could imagine until it warmed up.

    The new carb solved all that. Installed a new intake with a new divorced-choke setup. Now starts up immediately and idles great. Also, make sure you get Doug Roe's book on Rochester carbs. It'll show you that Quadrajets are not that difficult to tune after all.

    <font color=blue>//////
    http://blazer79.coloradok5.com
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  3. Blaze

    Blaze 1/2 ton status

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    I don't know if they are they make something for 4x4s, but I've got a friedn with a 69 Chevy Truck with a 396 in it and he had similar problems. He put a Demon Carb on it and has never had a problem yet. I know they make them for street/strip applicatiions, but don't know if they are good on a 4x4.

    [​IMG]http://www.ncclassics.com
     
  4. Burt4x4

    Burt4x4 3/4 ton status

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    I'll second that on the Edelbrock Q-Jet 750cfm #1901 is what I have and for the last 5 yrs now I have had great performance and no real major problems. Did take a few trys to get the tuning right but now I have a farily good Idea on how it should sound while tunin and that helps alot. As far as terin it apart it real ain't that hard as long as you take your time and put it back together the same way it was taken apart then its just a madder of time.......
    good luck


    72K5[​IMG]Led Zeppelin[​IMG]Rock ON![​IMG]
    http://www.burt4x4.coloradok5.com
     
  5. Grim-Reaper

    Grim-Reaper 3/4 ton status Author

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    Sounds like your choke in improperly adjusted to me. If the Choke is hanging it would cause a rich condition that the idle screws will not correct for. Most auto parts stores have a book call "Rochester Carbs tunning" (Think thats right name). If the problem is not choke related than there is a leak in the float bowl or the meetering rods are hung. Could also be vacume related. The primary rods are closed with vacume to kick it back to the idle jets. Once the vacume drops when you open the throttle the jets open.
    Unless your ready to go FI I would stick with a Quad. They are the best off road for the bucks and once dialed in they need almost no attention other than a occasional hose down with carb cleaner to keep the external linkages free.

    Diging it in the dirt with my K5's
    Grim-Reaper
    http://grimsk5s.coloradok5.com/
     
  6. Boss

    Boss 1/2 ton status Author

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    Sparky,
    I'm gonna have to jump on the bandwagon and tell yah Quad is the only way to go. I had the same problem as you (hard start in cold and running too rich and wouldn't lean out). well, Instead of rebuilding it, I found a good deal on a Edelbrock Quadrajet #1903. Then I put in the Electric Choke kit for it and man, hard starts is the thing of the past. Starts like a damn FI truck.
    I also noticed performance gains. The truck now seems like it has more power then before. I'm told that the edelbrock quads have bigger jets in them then the Rochester, but not sure if that's true. But I'm also getting better gas mileage too (b/c not running rich anymore). Good luck
    Boss
    http://www.boss.coloradok5.com

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  7. Blue85

    Blue85 Troll Premium Member

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    If it is running rich all over the band, adjusting the screws won't help, since they only affect the idle circuit.

    It is probably easier overall to troubleshoot and tune your existing Q-Jet than it is to replace it with something else and then tune that, unless everything on the carb is really worn and you want to save a time-consuming rebuild. A rebuild kit is pretty inexpensive and the job really isn't that hard. Plus, it gives you a chance to soak out all of the crap that's built up in there over the years. Should save you $200 easy over a new carb.

    Check on the choke settings and all of the thermal-related vacuum lines, heat riser and whatever else changes with temperature. Also, if it always runs rich, check for sticking rods or a problem with the power piston.

    When a Q-Jet is working right, it will give you maybe the best mileage of any carb that is well-suited to your V8, due to it's small primaries.

    New 4x4 driver: "A lot of money in that truck, eh?"
    Me: "Oh, about 1/4 of a new one"
     
  8. realsquash

    realsquash 1/2 ton status

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    There is no voodoo to get a q-jet to work correctly. Most carbs will act that way to some extent because the choke is closed and will not allow enough air in. It's like running your 350 with a carb from your lawn mower when it's choked (and richer). Either rebuild yours if it is a good core, or buy a new q-jet from edelbrock or jet. Or put efi on it :)

    Squash
    http://www.trailrunners4x4.org/users/realsquash
     
  9. realsquash

    realsquash 1/2 ton status

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  10. Sparky

    Sparky 1/2 ton status

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    Thanks guys. I think the problem is related to vacume in the carb because if I give it enough gas sometimes it will clear itself out and go. I am pretty sure it is not choke related though. I guess i will rebuild the carb I have or get the Edelbrock. How much is the Edelbrock Quadrajet? What is a good way to tell if my carb will be a decent core to rebuild? Thanks all.

    Sparky

    78 K-5
     
  11. Wheels

    Wheels 1/2 ton status

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    Check those vacuum lines. When I tore my K5 down last december, I found dry rotted lines all over the place. Mine used to run like crap even after I tried a tune up and tried to adjust the mixture. The other place to look is the throttle body plate at the bottom of the carb. The rods that turn the butterflies are steel and the body is aluminum. Mine had a lot of play which made it run lean and have a rough idle. To adjust the mixture properly, you have to use the propane trick (see a chiltons manual for this procedure). The overall mixture screw is not located on the outside but under a small cap right in front of the vent horn. There is a small step on the side of this screw that should be flush (for passenger cars and about 1/32" above for a truck). I found this out from a carb shop after I tore mine apart and found no reference to it in any manual or even the instructions with the kit. After the rebuild and proper adjustments, starts and runs like a champ. One other thing, the floats are a composite foam type material that over the years will start to saturate with gas and will need to be replaced. If you rebuild it, have an extra set of hands available to hold the secondary metering rods and guide them when you put the top back on. The only problem I have now is the electric choke which seems to quit working when it rains.?????? Going to hook a dedicated ground wire from the choke to the engine tonight to see if this cures this. Of course now it wont rain.
     

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