Close



Results 1 to 7 of 7
  1. #1

    Default ***Inconsistent Idle***

    I am running a recently rebuilt Autolite 4100 carburetor and the stock Duraspark II ignition system in my 1985 302.

    I warmed the engine up and set the idle and the dash pot at 750RPM. It idles great here, until I take it for a spin. When I come back, the idle is up to 900RPM. I give it a quick stab of the throttle, and it comes back to 750RPM. Another test drive, and the same thing happens again. I pulled the air cleaner and it appears that the throttle isn't returning all the way to the dash pot setting. If I manually push the throttle arm down to the dashpot, it idles fine again at 750RPM.

    I take it for a spin again, and the same thing happens. Frustrated, I turn it off for about 30 minutes. Go back to start it, and it stalls immediately. Try it again and the engine starts right up but now it is idling low at 500RPM (but touching the dash pot that was previously set at 750 RPM) and is about ready to stall. So I give it some gas and the idle comes back to 750RPM and stay there until I drive it again or rev it up high and then it wants to idle at 900RPM again. I have to give the gas a quick stab again to get the throttle to return to 750RPM.

    It was running perfect until yesterday, and the engine was rebuilt only a couple of weeks ago.

    What in the heck is going on with this thing?
    Last edited by RickFury; 10-06-2011 at 08:20 PM.

  2. #2
    FEP Member 8ballEinstein's Avatar
    Join Date
    Jun 2010
    Location
    Southern California
    Posts
    432

    Default

    I'm not that familiar with this carb but if the throttle isn't returning to the dashpot setting then possibly the throttle plates are binding in the bores.

    This make me wonder, what happened to the stock 4180 carb?

  3. #3
    FEP Super Member bwguardian's Avatar
    Join Date
    Jul 2010
    Location
    Houston (Clear Lake), Texas
    Posts
    3,649

    Default

    You might also check the throttle cable for binding. Just disconnect the cable at the carb and see if you can figure out if the issue is with the carb or the cable.
    HAD
    '82 GT monochromatic (red)...black cloth

    HAVE
    '85 GT vert two tone (white on charcoal)...white leather
    '00 F350 two tone (white on silver)...gray cloth
    '00 Excursion Limited two tone (white on tan)...tan leather...wifes ride

  4. #4

    Default

    About the cable binding. Where do I start? How do I check the throttle cable? I already checked the return spring, and it has plenty of tension to push the throttle back to the dashpot. Is there anything else to check? The carburetor is an almost new unit from Pony Carburetors, so it shouldn't be the carburetor, but I guess anything is possible.

  5. #5
    FEP Super Member 85GT-79FJ40's Avatar
    Join Date
    Jul 2006
    Location
    Brookfield, NH
    Posts
    4,524

    Default

    I had this problem with the original 4180 on my 85. I didn't have a problem with the cable or throttle shafts binding I had a problem with the A/C kicker resting wherever it felt like it. I took it off and fabricated a solid throttle stop and that fixed it. But I put a regular Holley on it shortly afterwards.
    84 Capri RS
    89 BMW 325is
    2 Toyota 4x4's

  6. #6

    Default

    I don't have an A/C kicker, so that is not the cause of the problem I am experiencing.

    If the distributor was switching from ported to manifold vacuum, causing a low and then high idle, will that cause the throttle position lever location to move on the carburetor?
    Last edited by RickFury; 10-07-2011 at 10:37 AM.

  7. #7
    FEP Super Member bwguardian's Avatar
    Join Date
    Jul 2010
    Location
    Houston (Clear Lake), Texas
    Posts
    3,649

    Default

    Quote Originally Posted by RickFury View Post
    About the cable binding. Where do I start? How do I check the throttle cable? I already checked the return spring, and it has plenty of tension to push the throttle back to the dashpot. Is there anything else to check? The carburetor is an almost new unit from Pony Carburetors, so it shouldn't be the carburetor, but I guess anything is possible.
    ...and here probably lies your problem, do a search on them.
    HAD
    '82 GT monochromatic (red)...black cloth

    HAVE
    '85 GT vert two tone (white on charcoal)...white leather
    '00 F350 two tone (white on silver)...gray cloth
    '00 Excursion Limited two tone (white on tan)...tan leather...wifes ride

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •