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  1. #1
    Dwight Chew
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    Weber 38/38 tuning guide

    I was at the Bay Area 02 tech session this last weekend and one of the guys mentioned that there were two idle mixture adjustment screws on the Weber 38/38. This is the 1st time I've heard of it and sure enough there are what appears to be idle mixture screws on each side of the carb. Can anyone confirm and how the hell do you tune the sucker? Anyone have a tuning guide to the Weber 38/38 other than Haynes and Pat Barden's book?

    Anyone having problems with their electric chokes on their Weber 38/38s? I have 12v on the choke, but the choke doesn't seem to be doing anything. Now I thinking of converting the choke to a manual cable. Any opinions?

    Thanks for bandwidth.

    Dwight Chew
    '74 2002 (running just fine except for broken heater valve cable and electric choke problem)



  2. #2
    MartyR
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    My $0.02...if I may (long)


    I was at the Bay Area 02 tech session this last weekend and one of the guys mentioned that there were two idle mixture adjustment screws on the Weber 38/38. This is the 1st time I've heard of it and sure enough there are what appears to be idle mixture screws on each side of the carb. Can anyone confirm and how the hell do you tune the sucker? Anyone have a tuning guide to the Weber 38/38 other than Haynes and Pat Barden's book?

    Anyone having problems with their electric chokes on their Weber 38/38s? I have 12v on the choke, but the choke doesn't seem to be doing anything. Now I thinking of converting the choke to a manual cable. Any opinions?

    Thanks for bandwidth.

    Dwight Chew
    '74 2002 (running just fine except for broken heater valve cable and electric choke problem)

    Dwight,

    The 38/38 indeed has two idle mixture screws, one for each throat. These are, like you said, located near the base of the carb on either side. To tune mine (which I have done MANY times before understanding the principles behind it), I like to turn the idle mixture screws all the way in (until a very gentle...GENTLE!!!..turning of the screwdriver no longer turns the screws) and then back them out 1.5 turns exactly. I bring the idle speed to about 900 rpm. This is achieved by turning the idle SPEED screw out (to decrease idle speed) or in (to increase idle speed). The idle SPEED screw is located behind the teeth on the back of the carb; its position is perpendicular to the engine's longitude. There is another screw behind those teeth, namely the FAST IDLE SCREW (for setting choke speed), whose position is parallel to the engine's longitude. This FAST IDLE SCREW is also right behind the choke, so it's easy to figure out which screw is which.

    ANYHOW, for idle mixture adjustment, you want to FIRST MAKE SURE that your choke plates are FULLY OPEN at normal operating temp (i.e.when the engine is warm). If they are NOT, then rotate the choke mechanism (counterclockwise, if I remember correctly) until those plates are FULLY OPEN at idle when the engine's warm.

    NEXT, get your idle to the point where the car JUST starts to hesitate at idle (i.e. lean the mixture by turning the idle MIXTURE screws inward, or clockwise, equal amounts). Then back the screws out just a tad so the engine idles smoothly again. By now your idle speed will be low, so turn the IDLE SPEED SCREW INWARD (clockwise) until you arrive at your desired idle speed (I like 850-900 rpm).

    As far as the choke goes, I converted to electric from water over the winter. Honestly, I liked the water choke more; the electric choke has never seemed to work right... BUT, when the engine is COLD (and OFF), tap the gas pedal and make sure the choke plates are almost CLOSED (i.e. "choking" the carb, letting less air in). You can adjust your choke (cold idle speed) by turning the FAST IDLE SCREW as I described above. Remember, this screw is located right behind the choke mechanism, so it's easy to find (though a little tough to get to with your typical screwdriver...shouldn't be a problem). The head of this screw faces the front of the car, whereas the idle speed screw head faces the passenger side of the car. Turn the FAST IDLE SPEED screw IN (clockwise) to increase your cold idle speed, and vice versa to decrease it.

    If you need clarification, please email me.

    HTH

    Marty
    '73 w/38/38


  3. #3
    Paul(at Maximill...)
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    idle mix basics on the 38mm...

    Here's how I attack idle mix on the 38/38 carbs:

    with car running - count how many 1/2 or 1/4 turns it takes to tighten the idle mix screw lightly against the fully compressed spring. Do the same to the other screw - split the difference - so each screw is precisely the same number of turns from fully seated/compressed spring position.

    Now - gradually - in 1/4 turn increments - tighten each screw - making sure that each screw is turned an equal amount. Basically you want as lean an idle as possible without sacrificing smoothness.

    I'm no expert on chokes - but I **think** you can adjust the spring in the electrical choke by looening the 3 screws that affix the plastic "hat" of the choke housing - and rotating it until the butterflies up top are open at full operating temp. (you're essentially twisting the coil spring in the housing) Then with car cold - adjust choke idle screw.

    Hope this helps!

    Paul
    Maximill...


  4. #4
    Dwight Chew
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    Muchas gracias for the info....eom

    nt

  5. #5
    Gil
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    Hafta ask a dumb question.

    Due to the orientation of the carb throats on a non-progressive carb like the 38/38, won't one barrel run a little leaner than the other due to differences in vaccuum level? Or is that of any consequence as long as the total mixture adjustment provides the right idling?

    Gil
    72 Tii
    + inquiring mind


  6. #6
    MartyR
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    Float bowl right in middle of both bbls...prob not


  7. #7
    MartyR
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    'n both bbls spaced evenly over intake man opening


  8. #8
    Tim in MD
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    My 38/38 likes Paul's tuning method...FWIW n/t


  9. #9
    MikeG
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    Re: Weber 38/38 tuning guide

    no real opinion on this, Dwight, but I have had the same experience as you with my 38/38. Got it from Ireland--been on the car about 5 months. Wish I would have gone with manual choke!
    MikeG
    72 02 electric "choker"

    I was at the Bay Area 02 tech session this last weekend and one of the guys mentioned that there were two idle mixture adjustment screws on the Weber 38/38. This is the 1st time I've heard of it and sure enough there are what appears to be idle mixture screws on each side of the carb. Can anyone confirm and how the hell do you tune the sucker? Anyone have a tuning guide to the Weber 38/38 other than Haynes and Pat Barden's book?

    Anyone having problems with their electric chokes on their Weber 38/38s? I have 12v on the choke, but the choke doesn't seem to be doing anything. Now I thinking of converting the choke to a manual cable. Any opinions?

    Thanks for bandwidth.

    Dwight Chew
    '74 2002 (running just fine except for broken heater valve cable and electric choke problem)



  10. #10
    WINGMANDWN
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    38/38 info needed

    I have a supercharged Honda GL1000 motor on a nine foot long Salt Flat bike with a new Weber 38/38 carb. I need tuning information for this
    set up. Of course no one else in the world but me would do this but I have no idea of what air jets to use in conjunction with what main jets
    other than they need to be the same in both barrels. Emulsion tubes is another whole issue as well. Anywhere I can find explanations of ratios
    used one to another in the complete carb setup or am I going to live the next two months starting and stopping, changing out all the possible
    combinations until I figure out what will work?! Anyone?!
    Reply With Quote Reply With Quote 162.158.59.105

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