A very good explanation of Weber carbs. | The Z Club of Great Britain
  1. The Z Club relies on the support of it's paid members - join the club or renew your membership here.

A very good explanation of Weber carbs.

Discussion in 'Tuning & upgrades' started by Rob Gaskin, Jan 28, 2021.

  1. Rob Gaskin

    Rob Gaskin Treasurer Staff Member Moderator

  2. Texasroadrunner

    Texasroadrunner
    Z Club Member

    I found that one a year ago and read it several times. Very informative and it helped me tune my DCOE 40's. I was able to get rid of the annoying 1,800 rpm bog without making the plugs black.
    My favorite chart was "The Ideal Relationship of the Three Fuel Delivery Circuits" and the color Idle jet diagrams below it. I have two O2 sensors. One on cylinders 1-3 and the other on cylinders 4-6.
    The dual AFR gauge on my console has helped me get the carbs responding well and the spark plugs a nice tan color with a clean and happy powerband.

    Texasroadrunner
     
    Rushingphil and SeanDezart like this.
  3. SeanDezart

    SeanDezart Well-Known Forum User

    Would you say that is much more effective than a single sensor at the junction of all 6x primary pipes ?
     
  4. Texasroadrunner

    Texasroadrunner
    Z Club Member

    He Sean, I do enjoy seeing the AFR numbers change while I'm adjusting the idle mixture screws on Weber DCOE's. Having two O2 sensors makes setting them more accurate since I make all 3 needles (cyls 1-3) the same turns out. Then
    I set the other 3 needles (cyls 4-6). If it was all six cylinders read by a single O2 sensor, it would be more difficult. The best info from the AFR gauges with Weber carbs is during the transition zone from idle circuit to Main, taken care of by the Idle jets. The AFR is very
    sensitive to different idle jet sizes. After an idle or main jet change and a long test lap, I pull a few spark plugs to verify what I was seeing on the gauges and how the engine responds. This method takes much of the mystery out of tuning. When the AFR reads too
    lean as in 17:1 there will always be a bog. Someplace between 13:1 and 14:1 is the sweet spot for power and good gas mileage.
     
  5. SeanDezart

    SeanDezart Well-Known Forum User

    Thanks - always interesting to learn how people 'tune'.
     
  6. franky

    franky Well-Known Forum User

    BMW have two lamba sensors on their engines. Well when they made proper engines
     
    SeanDezart likes this.
  7. SeanDezart

    SeanDezart Well-Known Forum User

    Its an option I can look into....easy enough to produce.
     
  8. franky

    franky Well-Known Forum User

    you just need to make sure your factory allow for the length of the sensor on the merge collector.
     
    SeanDezart likes this.
  9. SeanDezart

    SeanDezart Well-Known Forum User

    And angle - optimum of 40° ?
     
  10. jonbills

    jonbills
    ZClub Administrator
    Moderator

    I think anywhere above horizontal is "optimal".
     
    SeanDezart and franky like this.
  11. SeanDezart

    SeanDezart Well-Known Forum User

    Yes, so less than 90°.
     
    jonbills likes this.
  12. franky

    franky Well-Known Forum User

    you'll have to consult a specialist.
     
    SeanDezart likes this.
  13. SeanDezart

    SeanDezart Well-Known Forum User

    I forgot to say, vertical is not an option :)
     
  14. franky

    franky Well-Known Forum User

    have your factory got a car they can line it up on? Are there any s30's in china? Or if there are, are they being imported by 'new money' there? might be a growing market?
     
  15. SeanDezart

    SeanDezart Well-Known Forum User

    No, yes, I don't believe so.
     
  16. SeanDezart

    SeanDezart Well-Known Forum User

    Not an armchair hero then...
     
  17. franky

    franky Well-Known Forum User

    I'm not sure where you'll find any.
     
  18. SeanDezart

    SeanDezart Well-Known Forum User

    ...plenty on here but luckily, I know what I'm doing, have ramps and a selection of early to late S30s upon which to experiment.
     
  19. franky

    franky Well-Known Forum User

    at least you know where you fan find some. Good news.
     
  20. Fairlineguy

    Fairlineguy
    Z Club Member

    Isn’t that a upstream and downstream sensor either side of the catalytic converter
     

Share This Page