News

SOLVING LOW IDLE

Discussion in '308/328' started by absostone, Jul 28, 2019.

  1. Saabguy

    Saabguy Formula 3
    Silver Subscribed

    Mar 28, 2012
    1,399
    Shreveport, LA
    I am honestly concerned that none of the regulars with experience have chimed in, Guys? Steve?

    Don't stress over this, Weber carbs take some initial fiddling and then they are good for a very long time.
     
    absostone likes this.
  2. absostone

    absostone F1 Rookie
    Silver Subscribed

    Jul 28, 2008
    4,392
    Fchat
    I don’t mind fiddling. It’s the point of paying someone and now this
     
  3. Steve Magnusson

    Steve Magnusson F1 World Champ
    Lifetime Rossa

    Jan 11, 2001
    18,467
    Texas
    Full Name:
    Steve Magnusson
    I've already said what I know ;). With the idle mixture screws fully closed and it still idles (but at ~5 Kg/hr), he should try reducing the airflow down to the ~3 Kg/hr range in one carb (the idle speed should reduce some) -- then see if opening the idle screws on that carb has any (beneficial) effect to re-raise the RPM. JMO.
     
    absostone likes this.
  4. absostone

    absostone F1 Rookie
    Silver Subscribed

    Jul 28, 2008
    4,392
    Fchat
    Warmed her up closed all the mixture in two carbs. Idle went down to almost nil. Turned 1 mix on one more car and she died.
     
  5. absostone

    absostone F1 Rookie
    Silver Subscribed

    Jul 28, 2008
    4,392
    Fchat
    No it idles 5KG at idle with the original setting of the mixture Not with closed mixture
     
  6. Saabguy

    Saabguy Formula 3
    Silver Subscribed

    Mar 28, 2012
    1,399
    Shreveport, LA
    GOOD! so that tells us that one carb, the one you didn't touch was flowing NO fuel, that the last carb you changed mixture on was flowing enough fuel to keep car running, and likely that the first two were flowing more or less the right amount. Make sense?

     
  7. absostone

    absostone F1 Rookie
    Silver Subscribed

    Jul 28, 2008
    4,392
    Fchat
    Yes. I closed 5 barrels. But do you think 3 barrels would of kept 8 cylinders turning?
     
  8. absostone

    absostone F1 Rookie
    Silver Subscribed

    Jul 28, 2008
    4,392
    Fchat
    I will try it again but start with the carb I didn’t touch
     
  9. absostone

    absostone F1 Rookie
    Silver Subscribed

    Jul 28, 2008
    4,392
    Fchat
    I turned that one carb both screws in and the idle went down. I turned them out 3 turns and idle went up. Then I began to turn one of the barrels richer and the idle would raise slightly till around 4.5 turns. But idle didn’t change stopped at five turns but idle wouldn’t go down as if too much fuel.
    Then I tried another carb from the original settings I richened one barrel and this time the rpms were raising slightly.
    So am I reading my book and idle drawing correctly. Butterflies completely closed and air is drawn through the corrector/ main well but is bypassed through the idle jet. There is also the mention of a starter valve at play at idle. But I don’t understand it’s contribution to the idle circuits
     
  10. Saabguy

    Saabguy Formula 3
    Silver Subscribed

    Mar 28, 2012
    1,399
    Shreveport, LA
    So after idle speed raises by turning mixture screws you then have to back off idle speed screw to get to ideal idle speed then go through each mixture screw again. Rinse and repeat until if you touch ANY mixture screw the idle will slow. And I mean touch, making it richer or leaner will have the sam effect, revs will go down.

    Starter valve may be the extra jolt of juice when you first floor the pedal.. not sure about that one.
     
  11. absostone

    absostone F1 Rookie
    Silver Subscribed

    Jul 28, 2008
    4,392
    Fchat
    Another thing FYI. I turned one barrel all the way out from full in with engine off. There are approx 8-9 turns before the mixture spring looses contact. I thought someone stated 6.
     
  12. absostone

    absostone F1 Rookie
    Silver Subscribed

    Jul 28, 2008
    4,392
    Fchat
    I’ll try again and see if anything happens over 6 turns. I understand it should get to a point where it’s too much fuel then back of the 1/4-1/2 turn. Then reset idle and do the next barrel correct?
     
  13. absostone

    absostone F1 Rookie
    Silver Subscribed

    Jul 28, 2008
    4,392
    Fchat
  14. Saabguy

    Saabguy Formula 3
    Silver Subscribed

    Mar 28, 2012
    1,399
    Shreveport, LA
    Back the mixture screws out (Make it richer ) until the revs do not increase, use a good rev counter with a large scale if possible.
    Repeat on all of the mixture screws. ONE AT A TIME! The idle speed should now be higher.
    Back off the idle speed screw (s) to lower the idle to the desired speed. It will be in the manual but you can start at 800 or maybe 1000 revs.
    Now back out idle mixture screws again (Make it richer ), all of them one at a time. The idle speed should now be higher.
    Back off the idle speed screw (s) to get back to the 800 or 1000 revs.
    AT some iteration of this the idle speed will NOT get higher when you back off (richen) the mixture screw.
    Now slowly turn IN the idle mixture screw until the idle speed increases. Repeat for each mixture screw.
    Now back off the
    idle speed screw(s) to get to the ideal idle speed.

    The assumptions are:
    1. There is nothing wrong with the engine i.e. low compression in one cylinder
    2. There is nothing wrong with the ignition and the advance holds steady

    For this method you ignore the 1/4 turn, 1/2 turn stuff, those are gross means to get you started. This method will get you running well. It will take a while. You will go just a little blurry vision looking at the small graduations in the Rev counter.

    YMMV.

    Send pics of the carbs and linkages if you have the time.

     
  15. absostone

    absostone F1 Rookie
    Silver Subscribed

    Jul 28, 2008
    4,392
    Fchat
  16. absostone

    absostone F1 Rookie
    Silver Subscribed

    Jul 28, 2008
    4,392
    Fchat
    Ok so I’m getting a little confused. Shouldn’t the idle raise if richened. And then fall off if there is too much fuel and then turn back leaner and then adjust idle. Per barrel?

    And also. When/if throttle butterflies are fully closed doesn’t the idle stop screws open them slightly?
     
  17. absostone

    absostone F1 Rookie
    Silver Subscribed

    Jul 28, 2008
    4,392
    Fchat
    In other words richen one barrel at a time then back off leaner. If all the barrels are richened and it idles higher and higher. We are no longer at idle. 1k rpm
     
  18. absostone

    absostone F1 Rookie
    Silver Subscribed

    Jul 28, 2008
    4,392
    Fchat
    Ok so I played around with a few barrels. I went three turns out or more from the original settings. It seems like the idle does go up but slowly delayed. At 7 turns out are my idfle jets too small. ? I would think yes
     
  19. absostone

    absostone F1 Rookie
    Silver Subscribed

    Jul 28, 2008
    4,392
    Fchat
    Btw thx to you guys for sticking with me through this
     
  20. Steve Magnusson

    Steve Magnusson F1 World Champ
    Lifetime Rossa

    Jan 11, 2001
    18,467
    Texas
    Full Name:
    Steve Magnusson
    Then reduce the airflow rate to slow the RPM, readjust mixtures, readjust airflow, readjust mixture, etc..., until you are at 1000 RPM idle with reasonable mixture adjustments.
     
  21. Saabguy

    Saabguy Formula 3
    Silver Subscribed

    Mar 28, 2012
    1,399
    Shreveport, LA
    And disconnect the carb to carb throttle rods while you are doing this!! I didn't state that earlier and it is very important. You will be tuning each carb individually THEN you hook them all back together.

     
  22. absostone

    absostone F1 Rookie
    Silver Subscribed

    Jul 28, 2008
    4,392
    Fchat
    Wow. This is a lot more than I planned on based off of Birdman page
     
  23. absostone

    absostone F1 Rookie
    Silver Subscribed

    Jul 28, 2008
    4,392
    Fchat
    Reduce airflow side to side ? Front to back?
     
  24. absostone

    absostone F1 Rookie
    Silver Subscribed

    Jul 28, 2008
    4,392
    Fchat
    Okee doke will try that tomorrow. But my question still remains. If butterflies are to be fully closed, doesn’t the idle screws open the butterflies slightly?
     
  25. Steve Magnusson

    Steve Magnusson F1 World Champ
    Lifetime Rossa

    Jan 11, 2001
    18,467
    Texas
    Full Name:
    Steve Magnusson
    All (and they should be all the same).
     
    absostone likes this.

Share This Page