Best method to remove APT screw in baseplate?

Discussion in 'The Venerable Q-Jet' started by CJay, Apr 5, 2022.

  1. CJay

    CJay Supercar owner Staff Member

    I need to get my cruise a little richer so I want to be able to adjust my power piston. Any tips on successfully removing the factory screw in the base plate?
  2. Daves69

    Daves69 Too many cars too work on

    PM Cliff. I remember reading it somewhere. Either on here or in his book.
  3. Jim Weise

    Jim Weise EFI/DIS 482

    Soak the baseplate in a carb cleaner tank overnight. About 1 in 3 will then just turn right out.. the other two will have to have a little heat applied.

    In pre-75 carbs you need to replace the primary metering rods with the later tapered ones, to be able to effectively change the Cruise AFR.

    docgsx likes this.
  4. techg8

    techg8 The BS GS

    I wouldnt waste my time. I would swap out metering rods.
  5. TORQUED455

    TORQUED455 Well-Known Member

    Why do you think you need to get your cruise a little richer?
    dentboy likes this.
  6. Cliff R

    Cliff R Well-Known Member

    Yep, makes PERFECT sense to me, remove the carb from the engine, remove the airhorn, pop the power piston out, change the metering rods, and still find out once it's all back together you aren't exactly where you need to be.......OR.......remove the APT screw in the baseplate, install an external APT screw with a spring on it so it holds it's adjustment, and have full control from rich to lean WITHOUT having to take the carb off the engine or take it apart..........anyhow......Jim has it right, about 95 percent of the time they come right out with a little heat and penetrating out. I suggest two things, do NOT try to turn it without a good fitting screwdriver even if you have to make one, and be patient, most of them will come right out when they are ready. There will be one on occasion that isn't coming out despite your best efforts. I've removed at least 1000 at this point and about 1 or 2 in 100 just isn't going to budge no matter what you do.......

    IMG_4625.JPG IMG_4626.JPG
    Last edited: Apr 7, 2022
    69WILD, Dadrider and Dano like this.
  7. CJay

    CJay Supercar owner Staff Member

    It's not surging at cruise, but the plugs are white. The afr at idle is 13.5. I tried richening up the idle mixture but the plugs are still white. The car cruises around 2800. Im not sure when it transitions from the idle to the cruise curcuit. I haven't driven it with the wideband in it on the highway but I suspect the issue is cruise. I also like the convenience of being able to adjust the apt from a screw. Cliff did it to the aquamist cars carb years ago and it was the greatest thing to me since sliced bread!

    Since I'm new to removing them, the plug just pops out? And how much heat? Butane torch hot?
  8. TORQUED455

    TORQUED455 Well-Known Member

    Just like Cliff says - heat it a little at a time, cool it with Kroil, be gentle. You can also also try to turn it in to break it free if the slot becomes "compromised". Yes, you can drill a hole in the plug and pop it out with a pick or screw a screw in it and pop it out.

    Attached Files:

    Last edited: Apr 7, 2022
  9. CJay

    CJay Supercar owner Staff Member

    We'll give it a go this weekend. I'll cross my fingers
  10. LARRY70GS

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

    Unleaded fuel does not color the plugs like leaded fuel does. I replace my plugs once a year. 99% of the time, my engine runs on either 93 pump E10, or 91 non ethanol unleaded gas. At the end of the year, the plugs are light gray, or light brown, but I am sure if I removed the plugs after a month, they would be white.

    I have run my car with the AEM wideband for quite a while. At idle, it reads mid to low 13's. At steady state cruise, it runs at 14.6-15.2. I notice the non ethanol gas runs up to .5 richer across the board. At WOT, it reads 13.0. Never a complaint from the engine.

    The AED 1000 has shown 11.9 at WOT in high gear at the track.

    Jason, are you mixing the 110 leaded in at 50/50? It still might take a while to color the plugs.

    The APT adjustment is an awesome option to have though.
  11. CJay

    CJay Supercar owner Staff Member

    It's running pump gas in it and the plugs were white so....
  12. Cliff R

    Cliff R Well-Known Member

    "The afr at idle is 13.5. I tried richening up the idle mixture but the plugs are still white. The car cruises around 2800. Im not sure when it transitions from the idle to the cruise curcuit. I haven't driven it with the wideband in it on the highway but I suspect the issue is cruise"

    IMPOSSIBLE to read plugs to determine what's going on with these things. This new fuel, as mentioned burns so clean you are more often than not going to see light tan to white (unless you are using some sort of gas-guzzling aftermarket carb) try to look at them to tell which way to go with A/F.

    I don't even recommend a wide ban or even see the need for one. Idle is tuned for best idle quality at the leanest settings, doesn't matter what the A/F meter says. WOT is tuned for best ET/MPH at the track or engine/chassis dyno...but even with that said I ALWAYS er a tad on the rich side, keeps EGT's lower and less likely you'll put a piston in the oil pan!

    Part throttle is the most difficult to tune because you may see a wide range on your A/F depending on engine load, RPM, throttle angle, etc. Not uncommon at all to see mid-13's to as high as 16-17 to 1 A/F with a Q-jet and engine performance will be flawless clear across that range. In any and all cases we tune for results, not what a meter is telling us. I'd add here that Carburetors are not a "fixed" metering device, and change fuel delivery very effectively due to the venture principle combined with the items mentioned above plus pressure differential above and below the throttle plates (vacuum) and venturi/booster areas.........Cliff
  13. LARRY70GS

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

    Have you tried the Tip In procedure in Cliff's book?

    APT Tip In.jpg
  14. CJay

    CJay Supercar owner Staff Member

    You said at cruise, but what rpm since you have overdrive? My cruise is 2800-3000 rpm. With your set up you may still be on the idle curcuit and not on the main jet no?

    And the plugs that came out were whiter than white.
  15. telriv

    telriv Founders Club Member

    Myself the 1st. & easiest path is normally the better option so I would change the metering rods to richen it up by going a couple thousandths smaller on the larger diameter & see where that brings you. Easier than fouling with the APT & the associated problems that comes with it IF the screw breaks or the screw gets rounded.
    I think I would just try to hold up the metering rods with a piece of wire to see what that MAY bring you. Easy enough to do WITHOUT taking the carb. apart. Then it may give you a direction to go in IF it improves any.
    Just my thoughts.

    Tom T.
  16. CJay

    CJay Supercar owner Staff Member

    I think the wideband is a good tool. But it's just another data point. Combined with plug color, how the engine runs, etc. I wouldn't base my diagnosis based solely on the wideband
  17. LARRY70GS

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

    I'm at 2200 RPM @ 60 MPH.
  18. TORQUED455

    TORQUED455 Well-Known Member

    I’ve found the enrichment method, whether it’s your hand, the choke flap, or acetylene from the torch, to be most useful at idle for ferreting-out lean idle concerns. There are too many variables to properly tune part throttle/cruise at idle, IMO.

    Most Qjet issues that I’ve seen on normal, everyday stuff back in the day were indeed lean idling concerns. Cliff’’s techniques work miracles on these concerns, and I wish I knew about them 40 years ago.

    For stock applications, moving the APT adjustment to raise the primary metering rods to correct a symptom is usually just covering-up something else that’s wrong. But whatever works, works. After 50+ years, I wonder if the power piston spring has had enough?
  19. CJay

    CJay Supercar owner Staff Member

    In my humble opinion, if something is made with an adjustment, eventually it will need one
  20. TORQUED455

    TORQUED455 Well-Known Member

    Lol, that was the old saying for mechanics - if it has a screw, somebody will turn it!

Share This Page