New Rebuilt (by me) Quadrajet Runs like CRAP.

Discussion in 'The Venerable Q-Jet' started by MrSony, Jun 28, 2018.

  1. MrSony

    MrSony Well-Known Member

    I just don't get it. Its the EXACT same damn carburetor (17058241) that it replaced. The old one was worn out and kinda crappy, but worked alright. The new one (same number as the old one, the 17058241) was recently rebuilt by me. It. Runs. Like. Garbage. I'm furious to say the least. I've rebuilt at least 25 quadrajets and all have worked with great success, but this one is just a turd. It has a new needle and seat, float, accel pump, gasket kit, every thing you can replace in the carburetor has been replaced with the CORRECT parts. I've done this to the old carb in the past twice, and had great success. It will NOT idle below 1000 rpm, it revs up fine and quick (accel pump working) and it is really slow to idledown if i floor the pedal and let off quickly. It hunts for idle, idle screws do nothing. This carb was thoroughly cleaned, brake cleaner sprayed through every passage, wire pushed through every passage, this thing was SPOTLESS. I'm so damn angry that my old crappy carb that has been thrown down the stairs (by my little cousin) still works great compared to the one I just rebuilt. I'm about ready to throw the damn thing down the stairs.

    No there are no vacuum leaks.

    Timing is the same as it was, 8 initial, 22* advance, all in at 2800, untouched TA vacuum advance plugged into ported vacuum port. It just runs like sh*t and it really makes me mad. It's 11:17pm here. I've been f*cking with this thing for 4 hours. I have to put the old turd back on so I can get to work tomorrow.

    Gah! I wish I had a punching bag.
     
    matt68gs400, techg8 and TrunkMonkey like this.
  2. TrunkMonkey

    TrunkMonkey Well-Known Member

    If it runs with the "old turd" and not with the "rebuilt", then the problem is with the rebuilt carb. (and you already know this).

    The symptoms are vacuum leak. Everything you state hear is cumulative symptoms.

    " It will NOT idle below 1000 rpm, it revs up fine and quick (accel pump working) and it is really slow to idledown if i floor the pedal and let off quickly. It hunts for idle, idle screws do nothing. This carb was thoroughly cleaned, brake cleaner sprayed through every passage, wire pushed through every passage, this thing was SPOTLESS. I'm so damn angry that my old crappy carb that has been thrown down the stairs (by my little cousin) still works great compared to the one I just rebuilt. I'm about ready to throw the damn thing down the stairs. "

    "No there are no vacuum leaks." Yes, there is...

    You just have to figure out why it sucks so badly...



    FWIW, I am fighting with a similar problem with a 2x4 on my nailhead.

    Similar symptoms.

    Hunts idle.
    Idle mixture screws do nothing.
    Ported vacuum from "proper" bottom of rear carb.
    Vacuum at 650RPM is anywhere from 3 to 15 inches, depending on the idle raising and lowering.

    I replaced the front carb secondary throttle blades with brand new 15* correct blades and made sure they were slight loose and tapped the carb body to make sure they centered. After, no "daylight" with all the plates closed on both carbs.

    Throttle linkage/progression is adjusted correctly. All plates fully closed at idle, and the front trunnion set to one turn "loose", for "idle/closed" position, and full open, the trunion is set that all blades are fully opened at WOT.

    The shafts "feel" tight and no slop, and I did try both WD-40 and starting fluid to locate vacuum leaks, but the nearly 2-3 seconds from spraying and any upswing on RPM, "appears" to be from the fluid flashing off and being drawn through the venturies.

    There is not binding, choke works correctly. Starts within a second or two, cold or hot.

    But, I could make milkshakes with this thing at idle.

    When I set everything as it supposed to be, it will drop to about 200 RPM, then rise to nearly 1000 RPM then back down to 200.
    (Timing alternates from about 8*-14* corresponding to the hunting RPM)

    If I set it by closing the (big brass) air idle screw in the center of the rear carb, it will do the hunting and will buck when starting from a start in first or stall.

    I also blocked the brake booster/PCV port with a brass plug to test vacuum and eliminate as many sources for leaks on the carbs.
    The only vacuum source in use was the rear carb Vacuum Advance port, and no intake ports.


    If I am aggressive on the leave and keep it above 2000RPM, it is pretty happy, and very snappy and quick on acceleration.

    Runs solid at 187*-197*, and sitting in traffic will not get over 205*.

    No pinging at any throttle setting, but plugs (especially center four) indicate lean and are near white.

    Compression test shows 155-165 across all cylinders.

    New gas tank, EFI in tank pump, metered with Aeromotive regulator at the tank and return to the tank set at 4.5 PSI reading at the carb rail.

    I run 87 non-ethanol, but also ran 93 = or < 10% ethanol with no difference and not pinging.

    The best I had was with composite intake gaskets, (but I had them on backwards) and am using steel shims, both with copper sealant and the "blue" Permatex. (while waiting on another couple of sets of the composites).


    Rear carb intake bad has the exhaust heat plugged, and the passenger "exhaust butterfly" is removed.

    Running the correct 12* distributor, and Pertronix III and Flamethrower III with a 12V "resistor wire bypass".

    Set at 12* TDC initial.

    I tried closing the air idle screw and set the idle with a throttle idle stop screw to about 650 RPM, but after driving it and stopping at a traffic licht, the RPM will be up around 1000-1200 RPM then drop to about 800, and I still have to accelerate pretty aggressively away from the light.

    I also have a Q-jet intake/carb that I will try this weekend to see if it helps.

    Just so you know, you are not alone in fighting with gremlins. This is the first time I have ever had such a fight with carbs, except a Honda 750 Four F I had back in the 70's. It was a jetting issue when I bought it, and rejetting it fixed the problem, but it tried to kill me a couple of times before I fixed it.

    I will figure it out, but I pour sweat like a hard run race horse and the stuff is like Alien slobber, and will damn near eat through an engine block in seconds, so this heat has made it hard to do much troubleshooting.

    And I appreciate all the input Tom Telesco and Russ Martin have given me, so far.

    Good luck on finding your headache.

    This one has me stumped, and It will be a "smack the forehead" moment when I figure it out.
     
    Donuts & Peelouts likes this.
  3. MrSony

    MrSony Well-Known Member

    This new carb was an ebay find, supposedly rebuilt 20 years ago blah blah blah. I put it on for giggles, and looking back on it now, it kinda ran better before i rebuilt it. The ONLY thing I did was replace the primary rods with some from a 403 olds carb I had lying around. The Buick carb's passenger rod tip was broken off. Didn't have any on hand. It's too late now, only thing left I can try I guess is transplanting the rods and jets from the old carb into the new carb.

    And there is no vacuum leaks. The thing has 18" of vacuum at idle, steady. I bolted the old carb back on, flick of a key, and off I was. A vacuum leak would cause both carbs to run like ass, or at least appear to be.

    FYI, old carb idle screws are 2 turns out, idles at 800rpm dead in park, 600-550 in gear. Will idle itself at 35-38mph on flat road.
     
  4. MrSony

    MrSony Well-Known Member

    I wish you luck in your endeavors as well TrunkMonkey.
     
    Donuts & Peelouts likes this.
  5. Fox's Den

    Fox's Den 355Xrs

    Holley dbl pumper works like a champ and easy to work on.
     
  6. Taulbee2277

    Taulbee2277 Silver Level contributor

    A worn throttle shaft bushing is a vacuum leak and will drive you nuts.
     
    Last edited: Jun 29, 2018
  7. rkammer

    rkammer Gold Level Contributor

    Worn throttle shafts? Leaky well plugs?
     
  8. carmantx

    carmantx Never Surrender

    Take the primary rods out of your old Buick carb and put in the new one. Try that.

    The 17058241 would have had 73 Jets and 48K primary rods.
    Most Olds 403 Quadrajets had 52P or 55P primary rods.
    Changing out the rods changed up the calibration quite a bit.

    This doesn't help your high idle issue, but it is a start.

    You bought the new one on ebay. It may have been a commercial remanufactured unit. It may have idle bypass blocked in main body, APT lowered all the way, enlarged idle tubes and down channel restrictions.
     
  9. techg8

    techg8 The BS GS

    Sometimes it seems they just want to kick you around some. I've felt like you describe....
     
  10. MrSony

    MrSony Well-Known Member

    It's not that it's idling high on it's own, I have to make it idle high, or it wont run. It will spit and sputter. It's either 300rpm spitting and sputtering for 1100rpm and running ok.
    I'll swap jets and rods and report back.
     
  11. UNDERDOG350

    UNDERDOG350 350 Buick purestock racer

    There are several different gaskets that fit between the throttle plate and the main body/bowl. If you have the incorrect gasket there it will have a vacuum leak and run as described.
     
  12. 69a-body

    69a-body Well-Known Member

    Also check that body and air horn are not warped from overtightening. I have a rebuilt carb where they blocked air bypass passage with lead plug. And double check the hot idle compensation valve on back if it has one
     
  13. Fox's Den

    Fox's Den 355Xrs

    I think I would have bought a carb from one of the guys here that know the ins and outs of the Q-jet they are experts at it. You just don't know what you can get on evil bay. You can't go wrong if you go with one of our Q-jet men.
     
    Mark Demko and pbr400 like this.
  14. Mark Demko

    Mark Demko Well-Known Member

    Q-Jets kick ass:cool:
     
  15. Cliff R

    Cliff R Well-Known Member

    Fundamental issue assuming correct rebuild parts used and correct settings.

    I'd start by removing the baseplate and rebuilding it with bronze bushings, and spend some time centering/indexing the throttle plates. If a lot of air is getting by the secondary plates it will have all the symptoms described.

    Next remove and clean the idle tubes.

    Install new jets and metering rods and quit messing around with old worn out parts. New power piston spring as well.

    If you don't see an improvement it's quite likely something was modified during the previous "rebuild", like drilling some or all of the airbleeds out to large (I see this a LOT with anything commercially "rebuilt/remanufactured").......Cliff
     
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  16. MrSony

    MrSony Well-Known Member

    As far as I'm aware, it was just a carb that was rebuilt by a guy who maybe had a shop 20+ years ago, sat unused "rebuilt". The throttle plates seem to be indexed correctly. With the curb idle screw all the way out they will almost cover the entirety of the transition(?) slots. No light shines through either, primaries or secondaries. There are no throttle bushings. I have some, but I couldn't find my dremel stones to grind off the staked screw threads. I've rebushed my other carbs and the linkage was nice and firm afterwards. Not tight, but firm. These feel like that already, and no amount of moving the linkage and spraying carb cleaner could make it idle higher.


    Side note, anyone know a place where I can purchase the factory 48k rods (new)? Ebay I've had no such luck. Seen jets, and M4M rods, but no M4MC rods at all. Maybe I'm not looking hard enough...
     
  17. MrSony

    MrSony Well-Known Member

  18. shiftbyear

    shiftbyear Well-Known Member

    I doubt if your idle problem is caused by metering rods. Concentrate on the idle tubes, not only should they be replaced but possibly enlarged since the originals are sized for extremely lean 1978 standards. Also consider opening up the idle discharge opening to allow more fuel/air mixture with the adjustment screws. Ethanol added fuels require more fuel throughout the fuel curve. Cliff Ruggles books goes over these mods and sell the parts. The tubes are also available from other qjet vendors. idle tube.gif There is also youtube videos. Good luck.
     
  19. Greg Gessler

    Greg Gessler GS Stage1

    MrSony likes this.
  20. MrSony

    MrSony Well-Known Member

    Cool, Thanks Greg.
    I swapped in a set of factory 48k rods, runs better, but still lean. can pretty much cover the chokw housing and it runs better. I think I do need to do some more mods to it, but for now it's more than I care to mess with. Thanks for all the help.

    And shiftybear, I do have that book. I'll read the mods section once more.
     

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