Cautionary Tale of 20r Aisan Carb

Discussion in '1976-1983 Build-Up/Project Threads' started by Davo, Jul 26, 2020.

  1. Davo

    Davo Newbie

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    How many times have you read a thread where someone reported rough, high idle and, usually, gas dripping from the booster? Help! My mixture screw does nothing! Yup. That was me. I searched many a forum because this was the problem I had with my rebuilt 1978 pickup's 20r. New stock carb, vacuum hoses right, rebuilt head, all stock emissions...I tried everything. Well, almost. After 2 months of reading and learning, 5 repair manuals and the FSM, I determined that my idle circuit was not operating. I will end the suspense. Wasn't a vacuum leak or a clogged port. It was...drum roll, please...the electric idle stop solenoid. I read in one place that since my year wasn't equipped with a plug for this, just ignore it. I finally figured out that it plugs up the idle circuit...Aisan apparently underestimated our ability to fiddle with the carbs various screws until it would run and sort of idle even with the circuit blocked. Needless to say, once I applied power and ground to this solenoid, the mixture screw magically started working. My truck now idles perfectly and quietly at 900 rpm. Well, if you understand this post, feel free to add your story or elaborate further on anything I missed.
     
  2. Davo

    Davo Newbie

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  3. fred heath

    fred heath Veteran

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    1978 Toyota Galavan Motorhome.
    Aisan carbs are a PITA. So many things that can go wrong. I switched to a Weber 32/36 and couldn’t be happier.
    Glad it worked out for you.
     
  4. Cocolux

    Cocolux Newbie

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    I'm having a similar problem, looking at a Weber right now. Thanks for alerting me through your own findings.
     
  5. Davo

    Davo Newbie

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    I actually got the truck to pass California Smog! Everything stock. Passed with like new number, the tech said.
     
  6. Cocolux

    Cocolux Newbie

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    Geez, that's pretty cool. My coco is stinking of fuel at the moment. I have a rebuild kit but not sure if I should waste the time. Did you rebuild yours Davo? Cheers. Ben
     
  7. Davo

    Davo Newbie

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    [​IMG]
    DavoNewbie
    I did. Make sure the fast idle screw is not in too far. If you see any gas coming from the booster, it is not adjusted right. The flap butterfly thing, I forget the right names, should not allow enough suction during idle to activate those. All the gas and air should come from underneath it where the idle circuit ports are
     
  8. Yusuf RN20

    Yusuf RN20 Newbie

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    Hi there. I am new to this forum. I think i may have a similar issue. Do you have pics of the wire and how you fixed it.
     
  9. Davo

    Davo Newbie

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    Hey there, Yusuf. I will get some pics today. I have to adjust my valve lash, anyway. Stand by for later.
     

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