78 Aisan Carburetor Idling from secondary Venturi?

Discussion in '40- & 55-Series Tech' started by Kimber24, Jan 23, 2012.

  1. Kimber24

    Kimber24

    Messages:
    8
    I have a 75 Fj40 that ran great with a Holley 2 barrel, but I wanted the oem look and realiabilty offroad so I bought a 78 Aisan to rebuild. The PO had completely desmogged the truck, but I do have 12v running to the idle solenoid.

    The carb was dipped using Berrymans Chem Dip, the passages were then cleaned again with carb cleaner and then blown through with compressed air. I reused the jets, springs, etc. New gaskets, check balls, and seals were used. Fuel level is perfect on the sight window. Full return is capped at the carb.

    The truck will start easily but only runs at a very high idle (2,000 rpm). I have been unable to get the idle down by adjusting the high speed, partial speed, or low speed adjustments.

    I looked inside the carb while it was running and the secondary Venturi was spraying fuel but not the primary Venturi. The primary sprays fine from a small nozzle in the corner of the primary with the engine shut off. The secondary and the primary butterflies are both fully shut. I have never encountered this before and didn't see any discussion on the forums from anyone else having this issue.

    Any help would be appreciated.
  2. krzyabncanuck

    krzyabncanuck GOLD Star

    Messages:
    7,748
    Location:
    NC
    Have you heard the Idle solenoid click ?

    Do you have a vacuum leak now around the base of the carb ? Forgot to hook up a vacuum hose ? Who built the carb for you ? Could of missed something inside of the carb like one of the passages. Jets fully cleaned out ?
  3. Kimber24

    Kimber24

    Messages:
    8
    The idle solenoid does click. I am running it off of the battery as a way to test it. The needle inside the solenoid doesn't seem to move in and out but rather from side to side. Not sure if that is correct.

    I rebuilt the carb myself. I have a lot of experience on Quadrajets but this is my first Aisan rebuild.

    New gaskets at the base. No idle adjustment is evident when sprayed with carb cleaner at the base.

    Something that does come to mind is the gasket on the air horn did cover the pump disc. ball stopper. I'm not sure if that is correct, but it was the only way the gasket could be turned to fit.

    All jets and passages were cleaned thoroughly. Not to say that couldn't be the root of the problem.

    Pics are attached. Vacuum lines and throttle linkage is disconnected in the pics. Since this is desmogged, I could use some help on the correct vacuum attachments for the carb. The dizzy is not running any vacuum at all.
    image-606471431.jpg image-1249173855.jpg
  4. Others have reported that the idle circuit doesn't work if the gasket is installed upside down.
    Did the gasket look like the one that you removed?
  5. Splangy

    Splangy SILVER Star

    Messages:
    4,305
    Location:
    New Hampshire
    The airhorn gasket is supposed to cover the discharge ball stopper thing. No gas or air goes through the stopper and you can't put the airhorn gasket on backwards or upside down. You just can't.

    Post up some pictures of the linkage on the other side of the carb.
  6. Kimber24

    Kimber24

    Messages:
    8
    When I took the air horn off, the old gasket was in such bad shape it was impossible to tell. It came off in very small pieces as it was removed. All off the jet holes and passages seemed to line up correctly. I suppose it is possible that a passage was covered. I made very sure that the slow speed jets were clear when the gasket was installed

    What about the block from the gasket on over the top of the pump disc. ball stopper? Is that usual?
  7. Kimber24

    Kimber24

    Messages:
    8
    Pics attached of the throttle/choke assembly. My apologies on the positioning of the pictures.
    image-1369519921.jpg image-1229209402.jpg image-3333191555.jpg
  8. Splangy

    Splangy SILVER Star

    Messages:
    4,305
    Location:
    New Hampshire
    Just noticed that.

    That is definitely not correct. It should move in and out, not side to side. In fact, I can't picture how it could move side to side.
    Last edited: Jan 24, 2012
  9. You can test its function with a couple of wires with alligator clips. Run power and ground (to the case if it's a single wire solenoid) and try to blow through it. It should be obvious if its working.
  10. subzali

    subzali

    Messages:
    2,710
    Location:
    Denver CO
    First, you've got a vacuum leak at that tube running off the top of the air horn toward the brake booster. Cap that off. It also looks like your EGR tube may not be plugged off. That will be a huge vacuum leak as well.

    That port off the front of the carb that you have hooked to the gas filter - that is your Hot Idle Compensation (HIC). Try capping that off instead of running it to vacuum at the gas filter.

    Second, the secondary shouldn't be providing any fuel unless the secondary throttle plate is open (in theory). Is your secondary throttle plate open or closed at "idle"?

    Looks to me like you may have some funky linkage going on there, someone like Jim C. could say yea or nay immediately. Compare your 2nd picture of post 3 to this - it looks like your acceleration rod is bent, and you shouldn't have that spring there:
    [​IMG]
  11. subzali

    subzali

    Messages:
    2,710
    Location:
    Denver CO
    Add: the secondary throttle plate is supposed to be held closed until the primary gets almost all the way wide open. When the primary is almost full open, the stop rotates out of the way and allows the secondary diaphragm to open the secondary throttle plate. So I don't get what's going on with yours.

    By the way, where is the hose from your throttle positioning diaphragm going?

  12. Pin_Head

    Pin_Head

    Messages:
    11,699
    Location:
    OC, CA
    There are a lot of little things wrong with the carb that I can see, but they don't explain why it won't idle properly. The accelerator pump arm is bent and the bowl vent is not capped.

    It should not pull fuel out of the secondary at idle. If it does, then the secondary is open too much at idle either because the linkage is misadjusted or misinstalled. Correct this first. If it still doesn't idle, then either there is a problem with the idle fuel or a manifold vacuum leak.
  13. Kimber24

    Kimber24

    Messages:
    8
    I pulled the carburetor and checked or fixed what was suggested above.

    The idle solenoid did check out okay. Blowing into the end with the case grounded allowed air through and shut it off when power was disconnected. I pulled the power supply off with the engine running and it killed the engine.

    I straightened the accelerator rod to back to it's original shape, pulled all of the vacuum hoses that were connected and blocked the openings on the carburetor that were not plugged.

    Checked and cleaned the air horn passages, jets, accelerator pump, etc and recleaned the bowl and air horn passages again. I also checked the secondary plate to make sure it was completely closing.

    Reinstalled the carburetor and it is running on the primary side like it should. Yes!!!

    The idle is now running a little running too high when the adjustments are made as recommended on the linkages. Any suggestions there? I know, I should do a search, but you have all been very helpful with this issue I thought you might be able to help with the idle issue.

    At this point the carburetor is not a connected to any vacuum at all.

    Pictures of the reinstalled carburetor.
  14. Kimber24

    Kimber24

    Messages:
    8
    I can't attach the pictures because of a size restriction. I will try again tomorrow morning.
  15. Pin_Head

    Pin_Head

    Messages:
    11,699
    Location:
    OC, CA
    There should be no observable fuel coming out of the primary nozzle. It should be running solely on the idle port below the throttle plate with about 20 inches of water steady manifold vacuum. Idjust the main idle speed screw in the cast iron base and the idle mixture to 650 RPM using the lean drop method described in the FSM and see how it runs over the entire range of its carb operation.
  16. Kimber24

    Kimber24

    Messages:
    8
    It is running as you described above. No fuel is visible in either Venturi until the throttle is raised above a certain level. Then it is spraying out of the primary side.

    I will work on the lean drop tuning method you described above.

    Thanks everyone for all of your help!
  17. Kimber24

    Kimber24

    Messages:
    8
    By the way, I watched Pinheads YouTube videos on how to rebuild the Aisan carburetor and they helped a lot.

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