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Thread: Secondary/Transfer Slot/won't idle down

  1. #1

    Default Secondary/Transfer Slot/won't idle down

    What does that mean in dummy terms 25 to 30 of the transfer slot exposed? What is the transfer slot, please?
    Last edited by Ryan; 12-24-2012 at 12:16 AM. Reason: title change

  2. #2
    Join Date
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    Quote Originally Posted by Ryan View Post
    What does that mean in dummies terms 25 to 30 of the transfer slot exposed? What is the transfer slot, please?
    It refers to adjusting the primary throttle blades (idle speed screw) to expose no more than .025"-.030" of the idle transfer slots.
    They're located under the primary throttle blades - must remove carburetor to measure with wire. Common problem.
    If so, you'll need to open the secondary blades a little bit, in order to close the primary blades (to maintain desired idle speed).
    When the idle transfer slots are exposed too much, it renders the idle mixture screws useless.
    http://www.youtube.com/playlist?list=PL353239D6A7D7BFF0
    (Watch video titled "How To Adjust The Secondary Speed Screw".)
    May God's Grace Bless You

    '78 BRONCO: 508" stroker, TFS heads, Dominator MPFI & DIS, cold air induction, dual 3" exhaust/Magnaflow mufflers, 100HP progressive dry direct-port NOS, A/C, Lentech Strip Terminator wide-ratio AOD, 3:1 Atlas II, modified Dana 44/60-lockers-4.10s, hydroboost/4-disc brakes, ram-assist/heim joint steering, Cage long radius arms, custom traction bars, 4" lift, 35" mud tires

  3. #3

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    Okay, so I watched the secondary idle screw video. Makes sense, except my application does not match the facts stated. I'm not running a big cam that causes low idle vacuum. I have a 302 with a 351W cam. Don't know specs, but I get about 15 in-Hg of manifold vacuum. So by what the video says, I shouldn't mess with secondary idle screw.

    I did notice that my curb idle screw does not touch the throttle arm. It can idle higher but only go so low before it won't touch. When I push on the throttle arm, it idles down a little. I do not have a return spring, as I'm using the stock throttle cable (4 cyl Ford Mustang spring over cable). It must be in the idle circuit need to redo metering screws. Or it is indeed the secondary idle screw? My vacuum secondary adjustment can be done with a screw not the idle screw, that is located on the top of the diaphragm housing. It is marked with a sticker that reads F<====>S. Assuming that means fast or slow.
    Last edited by Danny Cabral; 12-16-2012 at 03:51 AM. Reason: misspelling

  4. #4
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    Quote Originally Posted by Ryan View Post
    So by what the video says, I shouldn't mess with secondary idle screw.
    That's not necessarily true. Is this a new or used carburetor? Which Holley carburetor is it (part number)?

    I did notice that my curb idle screw does not touch the throttle arm. It can idle higher but only go so low before it won't touch. When I push on the throttle arm, it idles down a little. I do not have a return spring, as I'm using the stock throttle cable (4 cyl Ford Mustang spring over cable).
    This problem needs to be corrected before any other tuning is performed.
    Every time the throttle is fully released, the lever should contact/stop against the idle speed screw.
    May God's Grace Bless You

    '78 BRONCO: 508" stroker, TFS heads, Dominator MPFI & DIS, cold air induction, dual 3" exhaust/Magnaflow mufflers, 100HP progressive dry direct-port NOS, A/C, Lentech Strip Terminator wide-ratio AOD, 3:1 Atlas II, modified Dana 44/60-lockers-4.10s, hydroboost/4-disc brakes, ram-assist/heim joint steering, Cage long radius arms, custom traction bars, 4" lift, 35" mud tires

  5. #5

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    It is a 670 cfm Pro Form which basically is a highly upgraded 4150 dual feed. I thought it was a double pumped until i read up on the differences. The carb is a year old and motor is two years (about 8 thousand miles). I never ran a regulator on it till recently. Had trouble getting discharge nozzle to quit leaking. HAD a tee line system for the return. But now I've got a very nice regulator with a return system the discharge nozzle operating with no leaks out the base but still having a idle issue. I still think I've leaned the idle circuit out to the point were it won't idle down. I will try a return spring and let you know. Maybe stock spring is too light. So should i be able to kill the motor with the idle screw no matter where i have the four corner idle set?

  6. #6

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    Okay so I enriched it a little. Car stopped popping out exhaust at idle. Put a stiff return spring and car idle at desired speed. But the spring is too stiff i don't like it. Throttle is too hard to depress. Spring came off garage door lock. (I'm garage door man) Im too cheap to buy the kit for $10. So my question is will the real return springs be stiff enough to return throttle and not make pedal hard. The ones at the store look too flimsy. Also my carb has secondary adjustment screw at the top of the diaphragm housing marked F<====>S on a sticker. I assume this means fast or slow for the secondaries to open up. Does this effect my idle too?
    Last edited by Ryan; 12-16-2012 at 12:23 PM.

  7. #7

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    Idle speed in no case should depend on what you doing here. Any normal carb installation on any car should have enough idle screw range that you can kill or nearly kill the engine. You either have a linkage/ binding/ butterflies problem or a VACUUM LEAK

    1--I would remove the carb and CAREFULLY check the on-carb linkage, IE choke, secondary, etc, as well as how the butterlfles seat in the bores. With the idle screws "out" the things should be nearly light--tight

    2--Check carefully for binding of the butterflies, either some obstruction on the manifold casting, or interferance with external linkage hitting the manifold or other brackets

    3--You should be able to run "all kinds" of advanced timing. My mild 318/360 Dodge, with the "rough equivalent" of a factory 340 cam, runs about 15--17* intitial advance, which ENCOURAGES a higher idle speed.

    4--Check for vacuum leaks with a scrap length of fuel hose held to your ear, probe around the carb base and other manifold fittings and listing for a "hiss." Also replace the PCV valve if any question as to it's condition. Take water in a spray bottle and "spritz" around the carb base. The idle speed will change if there's a leak. If your vehicle uses a vacuum modulator or other vacuum driven accessories (A/C controls, etc) check out the hoses carefully, and clamp them off with pliers to see if the idle changes. Don't leave out the power brake booster.

    4--Do not adjust idle speed with the mixture. You should be able to adjust for max RPM or vacuum at idle, then jog between the idle speed and mixture to tune the mixture for max RPM at your desired idle speed, ENGINE HOT. Then just "touch" the idle screws towards the lean side. Drop the RPM/ Vacuum just a tad, then come back CCW (rich) barely to bring RPM/ vacuum back up to a "peak." In other words, "lean" towards the "lean" side of the RPM/ vacuum peak.

    If the above results in a high idle speed, you either have a vacuum leak or still have problems with linkage/ butterflies binding

  8. #8

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    It funny you mentioned vacuum leaks cause my booster just took a dump when i backed in and out the drive to do those test. lol! I suppose i could just block it off for now to test. But i would like to also mention that i have a square/single plane intake air gap knock off. It never interfered with butterfly before now?! And I've been testing for vacuum leaks with carb cleaner. It seems even when i spray the intake directly it makes an idle difference perhaps cause its cooling it off. Is this not a good practice?

  9. #9

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    Okay got. Im an idiot. When i added the regulator to the fuel system i removed a vacuum line in the way and never hooked it up. lol! Brake booster works fine. Because of your reply i went to examine the booster fittings and pvc and that's when i saw it. Car idle as it should for a stick car 700 rpm. Now I've have to redo idle setting to make sure there not out of wack. Thank you for the advice. Just so you know i am a mopar guy at heart. I really like the A bodies but i had 72 roadrunner and miss it everyday.

  10. #10

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    So, sounds like you got' er pretty much squared away?

    I'm an old guy. Bought my first 69RR when I was in the Navy, Miramar, San Diego, in 1970. 71 or 72 bought a 70 440-6 RR, along the way, a former Pikes Peak, a 70 Cuda, 64 426 Dodge, and later, a 340 in my old Landcruiser. In my "old age" I've now got a 67 Dart. Was 273, then 360 (used, developed bottom end noise) now a 318, mild cam, Edelbrock Performer, and a used Holley Commander 950 EFI. I'm working on a home - modified manifold for mpi

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