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Help! Q-Jet question

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by Zeus33rd, May 1, 2002.

  1. Zeus33rd

    Zeus33rd Smarter than you GMOTM Winner

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    Ok, Just got this rebuilt Q-jet slapped on my truck last night. It's off a 76 Buick 455. It has an electric choke, where my old one didn't. Truck runs fine, idles fine and the new carb even fixed my hesitation problem. Anways, When I stuck it on the truck I didn't have any wire or anything on hand to hook up the choke. So I left it unhooked. Here's the problem/question I have....The secondaries won't open. Is this related to the electric choke not being hooked up? Or is there some other adjstment or something I need to check out? The truck drives just fine till ya mash the throttle, the transmission downshifts and your still on the primaries. Kinda gutless. I was fiddlin with it ealier and noticed that the choke pull off holds the the top plate above the secondaries closed. With the choke hooked up, will that allow that plate to open too? Basically I need to know what would cause the secondaries to not open and could this problemn be related to the electric choke not being wired. Thanks!
     
  2. Triaged

    Triaged 1/2 ton status

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    Yes...the choke has to be open for the secondaries to open.
     
  3. Zeus33rd

    Zeus33rd Smarter than you GMOTM Winner

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    Ahh.....lol, This electric choke thing is new to me. So thats all I have to do is wire in the choke?
     
  4. Zeus33rd

    Zeus33rd Smarter than you GMOTM Winner

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    Update......Wired the choke and no change. Was fiddlin with it a bit (with motor running of course.) and noticed that if I throttle it with the linkage on the drivers side, the secondaries won't open. But if I grab the little tang on the passenger side and turn it, the secondaries open. Along with the plate thing-a-ma-jig above the secondaries. Maybe I am making this more complicated than it needs to be.....But I really don't know much about cabrs....The terms and what to call certain parts. I'd approciate any info anyone can give me.
     
  5. txbluethunder

    txbluethunder 1/2 ton status

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    how do you know the secondarys don't open?? remember...they have to be under a load to open...which usually can only be done by driving it.
     
  6. Zeus33rd

    Zeus33rd Smarter than you GMOTM Winner

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    Well, I know for 2 reasons, One, I'm lookin at them through the top of the carb with the engine rinning, and Two, You just can't feel it or hear it when driving. My old Q-jet sounded like a jet takin off when they opened, this one does not.
     
  7. mudober

    mudober Registered Member

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    I think your choke pull off has to be working too.To check it, take the vacume line off push it in, seal the hole off with a wet finger, it should stay back, if comes all the way back out its shot.
     
  8. Jay73K20

    Jay73K20 Registered Member

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    The secondary on the Q-jet is mechanical, but they have an override spring on the throttle shaft. So if something is keeping them close they will stay closed. There is a little tab on the choke side that will keep them closed when the choke is on. You say you wired the choke up but didn't say it was working properly, is it? When the choke turns off make sure that tab (linkage) is free to move, that is where I would start.
     
  9. dyeager535

    dyeager535 1 ton status Premium Member

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    The "secondary lockout" tab is on the passenger side of the carb, and hits a pin in the secondary throttle shaft on that side. If the choke is "on" or linkage is messed up, the secondaries will be mechanically locked out. So that doesn't mean remove the tang, that means theres a linkage or choke problem that needs fixed, IF the choke should be "open", as in warmed up. If the truck is warmed up, and that lockout tang is disengaged (it just hangs there freely when it is) then go WOT with the truck off, and while doing so, watch the secondary throttle shaft....if the shaft turns, then the choke is off.

    Only the bottom of the secondaries are mechanically operated...at cruise you can still be "in the secondaries" but if vacuum is high, the air valve (the upper secondary "butterflies") will not be open, and you will still be on the primaries only.

    You won't see the secondaries open hardly any, if at all, when the truck is in park or neutral. You HAVE to drop engine vacuum enough to relax the pulloff. (works the same as vac advance, it falls off as vacuum decreases) That doesn't happen with no load on the engine. Engine demand (airflow) is what keeps the secondaries open, vacuum is what actually keeps them shut. Hence high vacuum readings=better mileage.

    The amount of airflow required to open and keep the secondaries open is governed by the tension spring on the passenger side top of the air valve, usually held under tension with a very small allen screw, and set with a flat blade screwdriver.

    Pulloff vacuum "loss" and therefore "quickness" that the secondaries open is governed by the orifice on the pulloff where the hose connects. The bigger it is, the quicker vacuum will be "lost" and the faster the secondaries are allowed to open, up to a point. Not likely its necessary to mess with though, but the tension spring MIGHT. Make sure the secondaries open before messing with it though.
     
  10. Jay73K20

    Jay73K20 Registered Member

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    Only the bottom of the secondaries are mechanically operated...at cruise you can still be "in the secondaries" but if vacuum is high, the air valve (the upper secondary "butterflies") will not be open, and you will still be on the primaries only.

    You cannot be in cruise mode with the secodaries open. The secodaries don’t start opening until the end of part throttle, your engine would have less then 4" (which is the lightest springs I know of) of vacuum which would cause the primary rod spring to overcome the suction of vacuum and cause the carb to go into power mode.

    I personally did away with the tension spring and drilled out the orifice in the pulloff valve. I then put a spring with a couple of washers and a nut over the air cleaner stud right on top of the secondary rod hanger. Tighten the nut and the secodaries don’t open as fast, loosen the nut and the secodaries will open faster. Easy adjustment just the way I like it:).
     
  11. dyeager535

    dyeager535 1 ton status Premium Member

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    Secondary throttle plates open at something like 60% part throttle, or 45*. IIRC.

    If it wasn't clear, I was trying to get across that the secondary throttle plate will open regardless of whether the secondary air valve is open or not, secondary throttle plate is governed entirely by throttle position or the on/off function of the lockout tang based on choke.
     
  12. Zeus33rd

    Zeus33rd Smarter than you GMOTM Winner

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    Now that I know what specific parts are called maybe I candescribe whats going on better. Ok, when I work the linkage on the drivers side with the motor OFF, the secondaries open. When I do this with the motor running, they don't. When I grab the little pin on the secondary throttle shaft and turn it, (which is a bitch, cause its hard to get a good enuff grip on turn) the pull off releases the secondary "butterflies", and everything works. What do I do next? lol..../forums/images/icons/crazy.gif
    And the electric choke....I wired it up, but I have no idea how to tell if it's working or if theres a way to adjust it.

    Maybe I'll just end up taking it somewhere to have someone work it over. Carbs give me a friggin headache.
     
  13. dyeager535

    dyeager535 1 ton status Premium Member

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    Ok if they work sometimes, but not all the time, that would indicate to me choke....the lockout tang on the passenger side is the ONLY thing that can prevent the secondary throttle plates from opening. (besides something mechanically wrong)

    The pulloff should relax because you are losing engine vacuum, at least AFAIK, without actually looking at it. That *should* be normal.

    I'd make sure that key off and key on, warm engine, the choke is fully open, and that the primaries are not on a fast idle cam. Is the electric choke held on with screws or rivets?
     
  14. Zeus33rd

    Zeus33rd Smarter than you GMOTM Winner

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    The little black cover on the choke is help on by 3 little screws. If thats what your talkin about. As far as the rest goes, I'm gonna spend sometime lookin at it tommorrow. Ijust got home about 45 minutes ago. I've been runnin all over the place today. Since I'm a welder, everyone has something they want me to weld for them. I went to three different buddies houses and welded different stuff for them. Good thing was that I got free beer at each place I went. /forums/images/icons/smile.gif Anyways, thanks for the help, And I'llcheck it out tommorrow and get back to ya.
     

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