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Idle jets/transition do matter - my Weber lesson this week

Discussion in 'Technical Q&A' started by snj5, Oct 26, 2004.

  1. snj5

    snj5 F1 World Champ

    Feb 22, 2003
    10,213
    San Antonio
    Full Name:
    Russ Turner
    Making errors so you won't have to....

    In my continuing effort to screwup a perfectly good running car by outsmarting myself, I decided to go down a size on my idle jets to cover a fairly rich idle istuation - (idling A/F in mid - 11s at 2 - 2.5 turns on the screws). It runs fine on 140/F24/190 if a bit rich. Well, changed the jets (55 to 50). It is also at this point where I made the agregious error of changing a couple of other things (like the fuel pump for a quieter model) in violation of the change only one thing at a time if you can rule.
    Well, synch'd up the carbs within 0.5 on the flow meter at idle and got a composite A/F at idle of mid 13s ( LM-1s rock!) with about 1.5 turns out on the mixture screws. Well, went to rev it up and she went way rough and lean at 5000 rpm with A/F climbing through 16. I figure running out of fuel delivery on the main circuit so I think "oh crap, a bad fuel pump". So, back on goes the Facet which had worked fine before, just a bit loud. Again, lean at 5000 running out of gas. So - Couldn't be the idles, it idles fine. Must be the fuel regulator as someone said they go bad. Verified that I can run the Facet without the regulator (4#), but same behavior. Crap.
    Put the 55 idles back in now figuring it must be a transition problem - well, all better - life is good.
    Those idles really do affect transition! Anyway, just a lesson learned for others that like to do Weber stuff.
    best
    rt
     
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  3. dr.mike

    dr.mike Karting

    Oct 31, 2003
    153
    Laguna Hills, CA
    Full Name:
    Mike Adams
    Just a note.

    The float levels are super critical to the idle/main transition. If the idles are still effective at 5000RPM, then the float level may be set low.

    lower float level = main circuit comes in at higher RPM
    higher float level = main circuit comes in at lower RPM

    If you have the LM-1 RPM converter ( or better, the AuxBox ), you can make an AFR vs RPM/MAP graph by recording a 3rd gear pull from 1000RPM up to redline. That really helps picking jets and setting the float levels.



    P.S.

    I am NOT an impartial source on the LM-1 and especially some of the accessories.
     
  4. Sean F.

    Sean F. F1 Rookie

    Feb 4, 2003
    3,003
    Kansas
    Full Name:
    Sean F
    What is the LM-1 ??
     
  5. snj5

    snj5 F1 World Champ

    Feb 22, 2003
    10,213
    San Antonio
    Full Name:
    Russ Turner
    the LM-1 is a wideband Air fuel meter that can computer download as well as correlate other variables such as rpm. I just got mine and am learning how to use it - it seems truely remarkable.
    It is very helpfulwith tuning mixtures.
    I got mine here from a fellow Fchatter:
    http://www.drivewerks.com/catalog/shopcart/TOOL/POR_TOOL_CAT447_pg1.htm

    No affiliation, yada yada...

    best
    rt

    Dr Mike - many thanks! All advice on how best to use this cool tool appreciated!
     
  6. pma1010

    pma1010 F1 Rookie

    Jul 21, 2002
    2,559
    Chicago
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    Philip
    Russ
    Did you try the F36s with the 55s?

    I also tried a set of 140 mains this week (140/F24/55/185). Went lean in the mid range. Back to the 145s.

    BTW, Mike at Pierce has been running 52s on his (stock) 79 308.
    Philip
     
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  8. snj5

    snj5 F1 World Champ

    Feb 22, 2003
    10,213
    San Antonio
    Full Name:
    Russ Turner
    Philip

    Will run the F24s and watch with the LM-1.
    I am then looking at swapping into 145/F36/200 and retesting. I have a good feel for the effect of main and A/C jets from the 10+ dyno sessions, but less of an appreciation for the emulsions (and until recently the idles). at the last dyno with 150/F24/190/55 the AF was pretty rich in the Mid range (11.5 - 12.3) The upper end never got above 13.4 We'll see - I am going to jet this for the stock airbox/K&N with it's inherent flow restrictions as I do plan to use this mostly on the street. I've found that with the airbox the A/F's are a bit more even (more even vacuum from aggregate effect I guess) and bring the A/F on the dyno .5 - 1 point richer across the range.

    best
    rt
     
  9. thecarreaper

    thecarreaper F1 World Champ
    Silver Subscribed

    Sep 30, 2003
    16,377
    Savannah
    Full Name:
    I NEED A JOB


    EXCELLENT thread, please keep us posted on your trials, errors and triumphs!! when my 308 arrives from the Left coast this weekend, it will be carb tech 101 all over again!!!
     

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