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Thread: Adjusting Order

  1. #1
    DX User
    Join Date
    May 2005
    Hi guys, some days ago I was having troubles with my carb, Keihin 2bbl, but I
    read a lot of post and that help me too much and I had resolved the problem.
    Now I have some questions
    1. What is the right order to set:
    idle control screw, mixture screw, throttle stop screw and fast idle screw
    2. Without removing the top hat of the carb Can I adjust the float level? Screw it Clockwise make it leaner or rich?
    3. What parts of the carburetor is responsible for the fuel consumption in normal revolutions or between 800 and 3000? I want the carburetor to help me spend less gas between this rpm.
    4. May be this is a stupid question!!! sorry. When the car is accelerated at 2000 rpm the exhaust pipe throw out less air than when is in minumum rpm 750<800 . Why? Does the engine breath for the exhaust pipe?
    Thanks. Martin.
    About my car.. is an Honda Civic EL 1993 (japanese version) 1343cc.

    Thanks for your help shepherd79.
    Hey last question!, Why the exhaust pipe expels water?

    Thanks Keachman1.

    What is better for a good gas mileage?
    1. Increase the RPM with the throttle stop screw and decrease the A/F mixture screw for example to get 900rpm
    Or the opposite
    2. Increase the RPM with the A/F and decrease the throttle stop screw to get the same rpm.
    Last edited by A20A1; 11-27-2005 at 10:32 AM.

  2. #2

    shepherd79's Avatar
    Join Date
    Apr 2002
    01 Civic lx auto; 03 Accord EX
    Falling Waters, WV USA
    1. i don't think there is an order for it. i always adjusted my idle screw to 1K RPM and go from there. if idle start dropping you can always bump it up with idle screw.
    2. the float level is adjusted from the top of the carb. remove the air cleaner box, and you should see yellow paint, or follow the fuel line to where it connects to the carb. Just becareful, too much adjustment and you can screw up the O-ring that is inside. if that happens, the fuel will start coming from the top around the screw. the best thing is to look at the fuel bowl window and make sure the fuel is in the middle or just a little above.
    3. to adjust the idle mixture, which is responsible for up to 3000RPM, you need to remove the carb, remove the plug that covers the idle mixture screw and put it back on the car. there is no other way you will be able to do that.
    4. I am not sure about JDM carbed engines, but in the US we had EGR system, that moved some of the exhaust gases from the exhaust manifold to intake manifold.

  3. #3

    A20A1's Avatar
    Join Date
    Sep 2001
    2006 Chevy Cobalt LS
    Kaneohe, Hawaii, United States


    (1) It's a good practice to be sure there are no vacuum leaks cause a vacuum leak will hinder idle adjustments and will mess up the fuel mixture and delivery.
    Some Things That Can Cause Vacuum Leaks
    - PCV Valve
    - Intake manifold and Carb Gaskets
    - Vacuum Lines
    - Faulty Thermovalves, check valves, or Solenoids
    - Leaky diaphragms
    - Leaky O-rings or internal carb passages
    (2) Also make sure your float level is set correctly.
    (3) Always check oil and radiator/coolant fluid levels before starting the car. This is good in it's own way but for the sake of idle adjusmtent, the themovalves require coolant in order to operete parts on the carb correctly.
    Also an overheating car can have idle and driving problems, and a carb not receiving coolant can have winter driving problems.
    (4) Another possible problem is a loose booster venturi, click here to find out how to check them.

    I adjust my carb the way listed below. This may not be how the manual/book does it.

    Just to let you know I don't have these things on my carburetor:
    - Fast Idle
    - A/C Idle boost
    - Choke
    However I'll include adjustment for the A/C idle boost.
    I also don't have more then that on my carburetor cause I removed many parts but for the sake of discussion I'll add on parts and show you when I adjust them.

    Remember most adjustments to idle speed or ignition timing are made with the car fully warm. The only cold adjustments are the FAST IDLE and CHOKE.


    First I start off by setting the base ignition timing, which is the Ignition timing without vacuum or rpm advance / retard. So you need to disable / disconnect both vacuum advances ; Vacuum lines #2 & #25.

    When disabling the vacuum advance you disconnect the vacuum lines to the advance diaphragm... these two vacuum lines need to be sealed so that they do not bleed vacuum and cause a vacuum leak while disconnected.

    Next set the ignition timing with a timing light aimed at the flywheel or plate on the torque convertor.
    Usually you won't need to disable #25 because all idle adjustments should be made with the car fully warm. When the car is fully warm there is no vacuum running thru #25 to the distributor vacuum advance port.
    Also the first idle adjustments should be made with the A/C and Accessories OFF.
    With everything off and the car fully warm, prevents the accessories, the choke, and cold start equipment form interfering in the idle adjustment process.

    The Prep , If you can't or don't know how to adjust ignition timing then proceed to STEP-THREE. However if ignition is your problem and you choose to skip adjusting ignition, then you'll just be masking your ignition problem with a higher idle.
    (1) Set base ignition timing ( Vacuum Advance disabled ) Refer to steps above !

    ... IMPORTANT. Remember, after you set the base ignition timing you need to reconnect the vacuum advance #2
    Quote Originally Posted by before or after
    You may choose to reconnect #2 after adjusting the throttle stop screw and before adjusting the idle controller diaphragm idle screw.


    You can connect #2 prior to adjusting the Throttle stop screw.
    Connecting #2 before or after adjusting the throttle stop screw will affect how your car will respond when there is a sharp drop in manifold vacuum.

    If you connect #2 after adjusting the throttle stop screw then a sudden drop in manifold vacuum wont bother the idle.

    If you adjust the throttle stop screw after #2 is reconnected then a drop in manifold vacuum can lower the idle past the throttle stop screw setting; although the idle diaphragm if connected should even out the idle.

    #25 can remain disconnected.

    (2) Turn out all Idle Diaphragm screws (If you need to temporarily raise the throttle stop screw... For Example if the idle droped way below 800 rpm )
    Here Are The Two Scews
    ... a. A/C idle boost screw
    ... b. Idle Diaphragm Screw ( Dashpot )
    * This will keep these screws from interfering with the throttle stop screw idle adjustment.

    Now it's time to adjust the idle speed

    (3) Set the Throttle Stop Screw to the Best & Lowest RPM idle speed.

    Usually this is about 500 - 800 RPM, but you may need it higher.

    Remember it is possible to set the throttle stop too high... too high meaning the throttle plate is open too far causing the carb to come off of the IDLE CIRCUIT. When the carb is off the IDLE CIRCUIT it has a hard time pulling fuel form the idle jet, and it could cause idle problems.

    3a.) Not that you should, but if you need to, now is the time to adjust the fuel mixture and see if it affects idle. I've adjusted the A/F screw on a weber carb so that the idle raises... and back off when the idle stops raising.
    3b.) Readjust the Throttle Stop Screw as needed.

    3d.) If you haven't already done so now is the time to connect #2 vacuum advance.

    4) Turn the Idle diaphragm until you reach a stable rpm... about 1,000 rpm the MAX is 1200 rpm in neutral... adjustment past 1200 is not recommended, and you should look elsewhere to fix your idle issues.

    Usually 1000 RPM in gear (automatic) or 900 - 1000 with lights turned on is a good idle speed.
    There is a second segment added to the body of the A/C idle boost diaphragm that aids in idle when the car is in gear.
    The vacuum port on this segment connects to vacuum line #21

    The idle diaphragm adjustment and A/C idle boost is partly to help automatic cars run when in gear and also aide both manual and automatic cars in idling when the headlights and regular interior fans are turned on.



    5) Keep the headlights and fans on and also turn on A/C
    Adjust the A/C idle boost to raise the idle speed back up to where the idle speed was prior to the A/C being turned on.
    BTW when I say turn on the A/C it should be at full blast.

    After the A/C idle boost is set you're all out of adjustment screws... at least ones for idle after the cold start process.




    IMO increased RPM to idle better with a proper mixture is better then a richer mixture to hold a Lower RPM. Though try to get as low a RPM as possible with a minimum of added fuel.

    Quote Originally Posted by POS carb

    4. this could be one of 2 things. a. you interpret the turbulent air coming out of the exhaust at idle as more VOLUME of air than at 2k rpms. this makes no scientific sense really but there is in fact an emissions component in these cars that is solely designed to pump fresh air into the exhaust pipe between exhaust strokes (it actually doesn't pump but runs on exhaust system scavenging effects and it is shut off by the "ecu" after a certain rpm somewhere around 2k like you said... you can hear it operating by removing that odd-shaped black pipe on the drivers side of the air cleaner)

    More heat and velocity perhaps???
    Hotter faster moving gasses are less dense so you feel them less or feel less of them?

    Quote Originally Posted by mcastro_m
    Hi guys, some days ago I was having troubles with my carb, Keihin 2bbl, but I
    read a lot of post and that help me too much and I had resolved the problem.
    Now I have some questions... ...About my car.. is an Honda Civic EL 1993 (Japanese version) 1343cc.
    Well 2bbl Keihin is a good sign... but I just read the part about it being on a civic. I'm beginning to think I may need to double check that all the components that I listed on USDM 2bbl Keihin are the same on your 2bbl Keihin. That way the adjustment procedure isn't confusing.
    Last edited by A20A1; 02-10-2006 at 03:38 PM.
    - llia

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