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Thread: Fast idle unloader

  1. #1
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    Fast idle unloader

    Hey guys,

    Can someone give me a good description of how the fast idle unloader works? What it actually does and when it's supposed to get vacuum? My understanding is that it has linkage to pull off the fast idle cam from the throttle linkage.

    Does it allow the throttle plate to close to the idle position?

    What are its vacuum sources? Are there any check valves or solenoids upstream of its vacuum lines that regulate the thing?

    thanks for any help you can give me.

    I'm trying to understand my carb better because it's doing some funny stuff.



  2. #2
    3Geez Veteran ACCORD EX's Avatar
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    ih you want to understand it better check the faqs too ! there are 2 faqs concerning the carb !

    MIKE
    3geez member since October 4th 2001

  3. #3
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    Yeah, thanks Mike. I checked out the faqs before, and all the work that people have done here posting pictures and explanations of our Keihin 2bbl carbs has been very helpful.

    But I'm still not sure that I understand the fast idle unloader -- what it does and when it's supposed to get vacuum and from where.


    -Greg

  4. #4
    LX User DanG86LX's Avatar
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    Fast Idle Unloader (FIU) is useful when the engine is started and left to fast idle (no gas pedal touching!), then when coolant reaches certain temps: (http://3geez.com/showthread.php?s=&threadid=6617), FIU pulls the fast idle cam which otherwise is stuck by a throttle valve lever. But when u tap the gas pedal or drive, the fast idle cam is free to follow (due to a little spring pull) the choke valve position.

    "What are its vacuum sources? Are there any check valves or solenoids upstream of its vacuum lines that regulate the thing?"
    Inspect ur vacuum diagram: http://www.angelfire.com/sd/bryhig/honda/vacdiag.html

    Not sure this is of any help to u though...

  5. #5
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    Dan,

    Thanks so much for all your explanations. They've been very helpful thus far.

    This is the condition that I have now:

    I disabled my choke opener (cut the arm & ran a cable to the linkage that I'm hand-choking from inside the car), and my setup is working fine, although I probably didn't need to do this as you pointed out before.

    All vacuum hoses are where they should be.

    Sometimes my high fast idle comes down from 2000 in 5 minutes -- (normal), but sometimes it takes 25 minutes.

    The temp has been COLD! here in Chicago in the morning, but roughly consistent. This morning it took 5 min to relax the choke to 800 RPM, but the other day it took 25 min.

    I'm suspecting erratic power to the choke heater or a loose ground.

    How does the power to the heater get its ground? If I understand this better, I'll either try to fix the ground or run an extra cable to another reliable ground just to be safe.

    Anyway, give me your thoughts if you got time.

    thanks so much!

  6. #6
    LX User DanG86LX's Avatar
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    The ground is the engine ground i.e. from Choke Heater (CH) metallic bracket => rivets/screws => carb body => manifold studs => manifold => engine block => battery(-). Jump wire from CH bracket to ground cable at cam cover. But i doubt the ground is ur problem cuz my electric choke behaves quite the same - intermittent. :pissed: I took it out and play with it for a while and then started to show continuity again ~ 25ohms. What is supposed to be inside is like a heater wire parallel with a thermoswitch and a thermister. I pulled a carb from junkyard with a good CH, just in case the old CH goes...
    Last edited by DanG86LX; 11-01-2002 at 07:57 PM.

  7. #7
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    Dan,

    You know, ever since I messed with my carb a few times a couple weeks ago, it's been working perfectly. Just one time afterward it took too long for the RPM's to drop to 1000. Otherwise it's been about 5 minutes, and it keeps getting colder in Chicago.

    The thing had been messed up for 3 YEARS! with the idle staying around 2000 for 20 min or more.

    I am starting to think that the linkage was just too sticky. When I inspected everything and messed with just a couple things (fixed one leaky vacuum line, made the choke opener into a cable pull-off opener), I cleaned the choke plate, inside the barrel, accelerator linkage, and also the choke levers and choke linkage with carb cleaner. I think that after the second time of cleaning it really thoroughly, the linkage moves very freely with very little friction or resistance.

    I think that my choke heater was working before but because of sticky linkage, the bi-metal spring had to get really hot and uncoil to the point where it had a lot of spring force before it overcame the resistance of the sticky linkage.

    Anyway, tell me if my theory sounds crazy to you, but I didn't really do much and now my choke mechanism seems to be working perfectly after years of malfunctioning in the winter.

    -Greg

  8. #8
    LX User joebeets's Avatar
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    If you have an auto, it's probably the throttle controller not retracting as it should when the engine starts. It's that rod on the same side as, and below, the FIU. You can manually push it in and your idle should drop.

  9. #9
    LX User DanG86LX's Avatar
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    Yeah, could be. But in my case i know choke heater was bad, i'll keep an eye on it..

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