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Who here likes to tinker with there q jets?

Discussion in 'The Garage' started by COCHEV, Jul 1, 2003.

  1. COCHEV

    COCHEV 1/2 ton status

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    i've got one that i just can't figure out. picked up a used one and, just for fun, threw it on the truck as is to see how it was. well after tuning to highest idle i could not lower the idle with the idle speed crew in order to do the normal lean idle drop. so i took it off and got a rebiuld kit and have had the damn thing on and off my truck like 10 times and still the same. plus it seams to make the truck idle rough which leads me to believe that i some how have some internal vac leak in the carb. so far this is what i have done to it: checked the base for straightness- its straight, epoxied the fuel wells, set the float as per the specs, intalled the kit (gaskets, accl pump, etc) and even tripple checked that i got the right kit and the gaskets matched. everything looks good except it looks like the P.O. took the butterflys off at some point and also removed the little deal on the secondary throttle shaft that keeps em from opening when the choke is on. still, it looks like the butterflys seal well when closed. so i'm stumped. the other q jet i have on the truck has been given the same treatment and runs perfect. oh, and yes, i check my timing and its correct and i don't seem to have any other vac leaks. anyone??? buy the way, this is an edelbrock 1904 q jet with electric choke.
     
  2. Don

    Don 1/2 ton status

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    Are the primary, and secondary throttle shaft's loose in their bore's? [vacuum leak] a normal Q jet problem. /forums/images/graemlins/eek.gif
     
  3. COCHEV

    COCHEV 1/2 ton status

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    well yes and no. when they are closed there is no play, when open, they can move side to side a bit. even my good q jet does this, as does another one i have setting around. so, at idle, which is where my problem is, the butterflys are shut and can not move side to side. /forums/images/graemlins/confused.gif
     
  4. Don

    Don 1/2 ton status

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    Any up and down movement in them, loose feeling?
     
  5. Don

    Don 1/2 ton status

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    As You probably know, Q-jet's run off of vacuum. Any vacuum leak and it will not operate correctly. Do You have the book by Doug Roe? Rochester Carburetor's, by Doug Roe. This book has everything You'll ever need to know about any Rochester carb made. From 1bbl, to electric Q-Jet's, it has it all, a must have for serious carb work. /forums/images/graemlins/grin.gif
     
  6. COCHEV

    COCHEV 1/2 ton status

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    yup, got the book /forums/images/graemlins/thumb.gif

    as for up an down movement, there is minimal movement if i grab the throttle linkage and try to move it up and down. again, i keep compairing it to my good carb and it seems to be the same. i know there are bushings available for the throttle shafts so i guess i could try that. i am also going to keep shoping for used ones so i can have some more parts. /forums/images/graemlins/grin.gif
     
  7. COCHEV

    COCHEV 1/2 ton status

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    you know the q jets by edlebroke have larger jets. do you think this could be part of the problem sense my motor is stock and wimpy? another thing that leads me to think this is that when driving with this carb i got a little bit of backfire on deceleration that i do not get with the other carb.
     
  8. Don

    Don 1/2 ton status

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    Jetting could be a problem with a smaller engine. i have gone around and scrounged up alot of used one's just to get jet's, needle's, secondary hanger's, power valve spring's, all the little goodie's that are getting hard to come by.

    Picked up a plastic box, with a lid, which has around 16 seperate compartment's, to sort out the bit's and piece's.

    Hit Your local pick a part, and pick up a few carb's, usually around $12.00- $15.00 each, and watch the paper for car part's, yard sale's, Q-Jet's at yard sale's are $5.00 each. It's good and inexpensive way of having the proper jet's, needle's, etc. on hand. /forums/images/graemlins/grin.gif

    If You plan on doing any serious tuning, or just getting it to run decent, You gotta have the jet's, and other stuff, to change. And only change one thing at a time, so You'll know if it helped, or made it worse. /forums/images/graemlins/eek.gif
     
  9. 383Jimmy

    383Jimmy Guest

    Sounds like some of the problems I've had before when I found the top (airhorn?) plate of the carb warped. Some dork over the years usually over-tightens the front two carb mounting bolts. The top gasket will stay wet and seep gas no matter how you try to adjust the float. They're not worth the effort to rebuild at that point.
     
  10. JDBlazer454

    JDBlazer454 1/2 ton status

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    I'm sorry your having problems with that carb /forums/images/graemlins/confused.gif Q jets and me just don't get along for some reason. I hope you can get it figured out, you already got me lost on what maybe wrong with it and beyond what I would have had patience for.
     
  11. dyeager535

    dyeager535 1 ton status Premium Member

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    You shouldn't be into the primaries at idle, so that *shouldn't* be an issue. Did you pull the primary rods/jets and inspect them closely? How about the power piston spring? Not ungodly springy is it? (could keep the primaries feeding fuel)

    In the Roe book, he goes into tuning the primaries for a "big" cam, have you checked to make sure those mods haven't been done? IIRC, you increase the idle adjustment by boring out the holes, which on a smaller engine might prohibit you from being able to turn the idle down. Haven't experienced this myself, nor played around with it, but seems possible. (if Edelbrock didn't do this with their new carbs automatically.)

    Have you tried retarding the timing just to see how the truck runs that way, and if you can adjust idle then? I know the one carb works fine with the same timing, but it's easy to try/test.
     
  12. COCHEV

    COCHEV 1/2 ton status

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    [ QUOTE ]
    In the Roe book, he goes into tuning the primaries for a "big" cam, have you checked to make sure those mods haven't been done? IIRC, you increase the idle adjustment by boring out the holes, which on a smaller engine might prohibit you from being able to turn the idle down. Haven't experienced this myself, nor played around with it, but seems possible. (if Edelbrock didn't do this with their new carbs automatically.)


    [/ QUOTE ]

    i think this might be part of it too. lettin more air by at i'dle so you can actually tune the idle circute with a bigger cam. guess i could just go get a bigger cam /forums/images/graemlins/tongue.gif

    never played with the timing- only checked it to make sure it was were it was supposed to be.
     
  13. COCHEV

    COCHEV 1/2 ton status

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    JD, no worries /forums/images/graemlins/thumb.gif thats why it was a $20 dollar carb. was meaning to ask you if you had any others with electric choke? most electric choke models had the stupid electronic control crap on em, but no all.

    i like q jets. when they run right, they're awesome. nothing like the sound of those big secondaries opening up /forums/images/graemlins/thumb.gif
     
  14. Blazer1970

    Blazer1970 1/2 ton status

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    [ QUOTE ]
    JD, no worries /forums/images/graemlins/thumb.gif thats why it was a $20 dollar carb. was meaning to ask you if you had any others with electric choke? most electric choke models had the stupid electronic control crap on em, but no all.

    i like q jets. when they run right, they're awesome. nothing like the sound of those big secondaries opening up /forums/images/graemlins/thumb.gif

    [/ QUOTE ]

    If it is leaking around the primary throttle shaft (common problem as noted above), you can usually stop the leak and get it to idle down by pushing down on the throttle shaft (where the throttle cable connects). This will normally stop the leak since it is only a leak below the throttle plates that will introduce any extra air to the idle circuit (because the butterflies are closed). I have heard of people running them for a long time this way by changing the geometry of the throttle return spring(s) so that they pull down on the shaft when the throttle is closed.

    I just pulled two non-electronic, electric choke Q-Jets at the pick and pull. They both came off 1980 Cadillacs with the 6.0l (368) engine. Jetting should be very close for a 350 also.
     
  15. JDBlazer454

    JDBlazer454 1/2 ton status

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    I'll run out and take a look on the wall o' carbs and see what is there and will post what I find /forums/images/graemlins/grin.gif
     
  16. JDBlazer454

    JDBlazer454 1/2 ton status

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    I do have one more the other 2 I have are manual chokes. If you want it let me know (your the only person I know who wants to mess with these things /forums/images/graemlins/rotfl.gif ).
     

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