Q-Jet Quartet

Discussion in 'The Venerable Q-Jet' started by lemmy-67, Jan 17, 2012.

  1. lemmy-67

    lemmy-67 Platinum Level Contributor

    I'll take a look at the secondary hangers and post some pics.

    The GM chassis manual says the bronze sintered filters are for the smaller Buick V8s: 340s, while the paper filters are for the 400/430 V8s. I don't even use a filter in the inlet nut, I have a NAPA gold inline filter just after the fuel tank. I figured using the cheap paper filter was redundant, since the little gasket on it always comes loose and the filter body always seems to end up getting twisted & disfigured...doesn't seem to do very much.

    I'd use the new blue ethanol-resistant pump cups which are available. I've had all the others jam on me or fall off the pump shaft. I'm also using the shortest possible pumps to get the max fuel shot per stroke. My needle/seat setup is 0.125", so I'm getting good fuel flow with no leaks, stock float height at 9/32".

    I'm now setting up another 248 carb, and cannibalizing some of my older non-functional cores for the parts. This latest 248 Q-Jet ran great all the way down to Monterey and back for the ROA meet. I'm looking forward to having the rest of the car 100% functional in time for next year's meet in Kentucky!
     
  2. mrolds69

    mrolds69 "The Cure"

    Thanks for the info Lemmy! The pump that jammed was a blue seal accel pump. I noticed that the original seals were deeper. I don't think you can get them now. I don't know why the pump jammed, the seal looks good. I was able to free it, maybe it was just a speck of dirt. But it wasn't the seal distorting. The hangers have letters stamped on them, I think the 430 carb I have has an I. I was curious if the 430 hanger was different than the GS400 hanger, because your car is heavier + has is a larger engine.
     
  3. lemmy-67

    lemmy-67 Platinum Level Contributor

    I got a bunch of new blue accelerator pump cups from quadrajetparts.com, I threw out all of my others. My pump doesn't have the garter spring, so the pump cup just fits over the end of the stem.


    For the secondary rod hanger, I have 2 types. One is for the early-67 Q-Jet and the other is for the late-67 Q-jet:


    [​IMG]


    I can't see any noticeable difference between the two, except the early-67 model has a RP part number of 33787, and the late-67 uses a 33797. Both have the same spec for initial rod height when installed.
     
  4. 6WildCat5

    6WildCat5 Great Dale House Car

    I looked at that web page for the one I have on my 248... Don't know which size it is, but the one Cliff sent with the garter spring works real well..
     
  5. Cliff R

    Cliff R Well-Known Member

    Highly recomended to upgrade to the modern pump assembly. They use a garter spring to keep the pump cup in constant contact with the bore.

    A retainer is crimped on the top of the plastic assembly to keep the shaft from pulling out.

    They also use upgraded delivery and duration springs (ours are custom from our spring winder to our spec's), and a lower retainer location for improved efficiency.

    We install a custom high grade flouroelostomer seal on our pumps. We tested the blue seals from the supplier, and they will NOT hold up in ethanol. Went round and round with them about this, and they just wouldn't step up with better parts.......Cliff
     
  6. LARRY70GS

    LARRY70GS a.k.a. "THE WIZARD" Staff Member

    I believe the difference is where the hole for the rod is drilled. The hangers have letter designations. Should be stamped somewhere.
     
  7. lemmy-67

    lemmy-67 Platinum Level Contributor

    Okay, number five is off the car for now. Damn fuel inlet nut started seeping again, and when I tried to tighten it some of the threads on the carb body stripped. I've put number 4 back on, with the base plate from number 1 since the throttle shaft was binding on the original baseplate. More pics to follow.

    Number 4 has a new set of idle tubes installed, and the idle is soooo smoooooth now. I'm going to pull out & replace all the idle tubes on my other carbs, it makes a huge difference in idle quality and in the transition to the main system.

    Only issue with number 4 when I put it on was my secondaries were getting stuck open. The air door spring was at a decent tension, but sometimes my secondary was getting stuck and my idle went up over 2000 RPM. Pumping the pedal usually got it back down, but not a good condition for street driving. I changed the rod hanger, and the problem went away. I originally had the scuffed one installed (see above photo), now I have one with better plating in there. Problem went away.
     
  8. lemmy-67

    lemmy-67 Platinum Level Contributor

    Okay, here's number 4, back on the engine with a new set of idle tubes installed:


    [​IMG]


    Seems to run and idle fine, no seepage from the inlet nut at all. I transferred the little guard-tower for the choke linkage over...nice thing to have in place to prevent the air cleaner from hitting & bending the choke stuff. The rust on it matches the choke flap and air doors, so that's a bonus. ;)

    This one also has the baseplate from #1 with the new bushings, so it's pretty much re-done from top to bottom.

    I'm going to monkey with the air-door spring, it may be a little tight at the moment. This one has the the AU secondary rods, which are a touch more thin than the AYs I normally see.

    I also managed to land an excellent 7027241 core for about $40, it arrived today. No rust or corrosion, and it is just about complete. Only thing toasted on it was the pull-off, and the external vent cover was missing, but this one came with the guard-tower, which is a plus. I'm going to use the air-horn and base on the fresh 248 core I'm building...this one will be number six.

    No, you can never have enough spare parts for the chariot. I'm getting closer to the ultimate setup for this rig.
     
    Last edited: Sep 20, 2012
  9. lemmy-67

    lemmy-67 Platinum Level Contributor

    I switched to AY secondary rods, seems to smooth out the acceleration a little bit...or maybe I'm just imagining it. :) Still love the idle and pull off the line of this one...those idle tube change-outs are certainly worth the effort.

    Also, this carb works very well with the choke. I installed a new choke coil which I got from another member of the board. This one works best of the 3 coils that I have:

    [​IMG]
     
    Last edited: Sep 27, 2012
  10. lemmy-67

    lemmy-67 Platinum Level Contributor

    Number 6 (7027248) is now assembled and ready to go on:


    [​IMG]


    ...though number 4 is still idling and running very well at the moment. If any kinks or snags come up and I need to take it off, I'll give this one a try. It has 74 jets and 41 rods...may be a tad rich for my engine, but I can easily swap in a set of 42 or even 44 rods if necessary.

    The next project is my 800 CFM Q-Jet core which I am rebuilding:


    [​IMG]


    It is a 1972 Electra/Riviera/Centurion 4MV Q-Jet, number 7042240. It has 72 primary jets, 48B rods, and CT secondary rods. It has the rear vacuum hookup on the base plate which will work for my AIR pump connection, and supports the divorced choke. I have torn it down and soaked it, and it is cleaning up very nicely:


    [​IMG]


    [​IMG]


    [​IMG]


    [​IMG]


    I have already sleeved the primary shaft bores with the bronze bushings, and installed a 7027248 throttle shaft with the correct linkage for my switch-pitch. I just need to order some more pull-offs and misc. parts, and modify a spare fuel line to adapt for the front-inlet connection. All of my other carbs are side-inlet. Looking forward to trying this one out down the road.
     
  11. Cliff R

    Cliff R Well-Known Member

    The 72 Buick carbs is superior in just about every area to what you have been using. It will take a larger fuel inlet seat and smaller float and handle at least 7-8 psi fuel pressure without any issues. It has an APT system in the baseplate. I recommend carefully removing the factory APT screw and replacing it. We make a custom screw with spring to hold adjustments. Teamed up with the right metering rods, this provides the user/tuner with full control of the part throttle A/F from rich too lean, without taking the carb apart and changing parts. Just select the correct jet size, and the carb can stay on the engine for all tuning.

    I recommend upgrading the internals and going to the upgraded accl pump assembly. This new fuel is hard on parts, and the "blue" seals found on over the counter pumps will not hold up in it......Cliff
     

    Attached Files:

  12. lemmy-67

    lemmy-67 Platinum Level Contributor

    I've pulled the idle tubes prior to the soak, and have a new set ready to tap in...same with the accelerator pump cup: new blue one from Gessler's on the pump, along with the correct set of springs.

    However, I see no APT screw in the front of my base plate. There is a circular plug there where the screw may be located...how do I access it? Do I need to drill this plug out?
     
  13. 6WildCat5

    6WildCat5 Great Dale House Car

    Beware, Even the experts only get 4 out of 5 of those loose... I attempted the APT mod once.. the stock screw is behind that plug cap... and is replaced with Cliffs setup... If I remember correctly, I just punched a hole in it with a nail and pryed it out... Custom made the correct size specified screw driver tip, soaked and heated the baseplate screw area until I destroyed the screw head trying to loosen it, then attemped to drill the screw out, destroying that mod even further..... That screw is hardened.... Filled the hole with a good epoxy and replaced that cap permently... That one mod still has me stumped... and am afraid to destroy the other baseplates in my collection trying.... Just wish I hadn't done the primary throttle bushings in it first... I don't do enough 71-74 carbs to get practice removing those, and they can be set in pretty good, or at least the one I tried did... Thank You Cliff to the rescue, The modified APT baseplate you made me is the perfect tuning tool, tip in dials right in, tho, I should get a set of your custom rods and jets to go with it... Lemmy, your more than welcome to that messed up plate still sitting on my shelf, at least it's still at a stock setting.... but, all in all, I do highly recommend x2 with what Cliff says about it.... Get the APT to work and have full control.... Works great for me....
     
  14. Cliff R

    Cliff R Well-Known Member

    I'm near 100 percent with getting them out, but ALWAYS use heat BEFORE trying to remove the screw, or the ends will snap right off 95 percent of the time.

    There is always one here and there that woln't come out no matter what you do. Drilling them is a lesson in humility, as they are hardened screws and very difficult to drill on center.....Cliff
     
  15. lemmy-67

    lemmy-67 Platinum Level Contributor

    Hi Cliff,

    Thanks for the tips...if I can get the plug out and remove the screw, I'll definitely do the upgrade. I didn't see the APT screw kit for sale on your site, though:

    http://www.cliffshighperformance.com/parts.html

    Do you have a link for it? I don't want to attempt punching out the plug and extracting the factory screw until I have the new parts and instructions in hand.
     
  16. 6WildCat5

    6WildCat5 Great Dale House Car

    I think it's the same on your '67 430 as the 425's.. Another thing to look at is the bottom of the '72 plate on the passengers side.. It's narrower on that side compared to the 248 and earlier carbs and may not cover the entire exhaust U channel on that side requiring plugging it off if they haven't been already... also the fast idle set screw setup at that end of the throttle shaft may rub the edge of the manifold not allowing it to seat correctly... Can be removed if not used or a bit of grinding on that edge of the intake or spacer may be required to run it... Assuming this is for a stock '67 manifold.. Not sure if the older plates will work on the 69 - 74 carb bodies and what it may require... I know others have done it from reading old posts, but, personally haven't looked into it... Would be great if it was just a simple base plate swap and adapt the APT screw onto it... Pretty sure sometime in the '68 run they changed the manifold carb mounting to match the newer style baseplates...
     
  17. lemmy-67

    lemmy-67 Platinum Level Contributor

    Yes, the base plate on the 800 CFM is narrower than the one on the 750 CFM Q-Jets, but the primary shaft is the same length. I checked it with the 1/4" base gasket I currently use, and there is no interference with the choke/fast idle arms on the primary shaft. The steel shield which fits under the base gasket will still seal the smiley channel off and there will be no exhaust leakage. I'm re-assembling the 800 CFM carb with the new parts now.

    The more tricky thing will be changing out the fuel line. I can either buy a new steel line for a 72 Riviera, and wrap it with the insulation I used for my current line (keeps the line cool to prevent vapor lock), or cut an old line, flare the end, and run a rubber fuel hose to the fitting on the front of the carb.
     
  18. lemmy-67

    lemmy-67 Platinum Level Contributor

    I discovered that I missed something on that 4th 7027248 Q-Jet: the hot idle compensator in the back. I didn't have a spare cork gasket for it, and figured I'd need to pull one off of my other cores. Fortunately, I had some old 4MV rebuild kit parts left over from when I had my 1974 Chevy C20, and I found a spare cork gasket in there. I re-assembled the missing pieces last night. Now, this sucker is 100% and ready, with new pump springs along with all the rest of the new internals.

    Still, 428 carb #4 is running so well, I'm in no hurry to swap it out just yet. Maybe I'll try it out over the holiday.

    I'm thinking of converting my spare steel fuel line from a side-inlet to a front-inlet. The side-inlet ones are longer. All I'd need to do is re-bend one section, cut off the U-section which turns 180 degrees towards the side-inlet, and re-flare the end for the retaining nut. Has anybody performed this conversion before?
     
    Last edited: Dec 19, 2012
  19. Cliff R

    Cliff R Well-Known Member

    Call the shop to order our APT screw, they are not a "stocked" item, I make them on our lathe per order.

    Fill the HIC hole with lead and get rid of the valve and gasket. That deal never did work all that well, and a common source for vacuum leaks leading to poor idle quality.....Cliff
     

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