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Thread: Autolite/Motorcraft 2100/2150 Theory of Operation

  1. #1

    Autolite/Motorcraft 2100/2150 Theory of Operation

    Taken from an AMC manual (AMC also used 2100's, as did Chrysler on certain applications). Note the carb pictured has its choke pulloff integrated into the top casting (early 1970's) versus later models with choke pulloffs hanging off the back. 2150 is virtually identical except for variable sized air bleeds via rods activated by a cam on the throttle plate shaft.

    AMC2100Manual1.jpg AMC2100Manual2.jpg AMC2100Manual3.jpg AMC2100Manual4.jpg AMC2100Manual5.jpg AMC2100Manual6.jpg AMC2100Manual7.jpg AMC2100Manual8.jpg

    Bill Robertson

  2. #2
    My carb doesn't have metering rods. Were those a later feature?

  3. #3
    No metering rods in a 2100 -- all fuel metering (closed plate idle through wide open throttle) is done via the jets.

    What some people erroneously call "metering rods" are actually variable air bleeds. It was a 2150 modification to reduce idle emissions. The rods are not precise at all, but they serve their purpose: when the throttle plates are closed the air bleed is effectively larger, as the throttle plates open the rods raise up, reducing the effective size of the air bleed. A cam on the throttle plate shaft presses on the rod holder, raising it up as the throttle plates open. There is no way to adjust the mechanism. All "baseball bats" (what the air bleed rods are often called, due to their shape) are identical, irrespective of venturi size. They also are quite wiggly in their holder.

    If you've got a 2150 (which I thought you did), this is where the variable air bleeds are located:

    Comparison of fixed size 2100 versus variable size 2150 air bleeds:

    2100 is significantly different from carburetors that do use metering rods to meter the fuel, such as Carters.

    Bill Robertson
    Last edited by Greasy DeLorean Mechanic; 08-19-2013 at 11:08 AM.

  4. #4
    That's weird -- I think my carb has the rod that goes down but not the stuff on top of that screw. I'm not sure, though. I'll get a picture tonight.

  5. #5
    I've got a carburetor at the house that I soaked and plugged unused ports, but I've been holding off painting the linkages because a solenoid is supposed to be on the way (I don't want to scratch paint off the throttle linkage test fitting a solenoid bracket) -- is the solenoid coming or not?

    Bill Robertson

  6. #6
    It is ready to go, but I haven't had a chance to get to the post office yet.

  7. #7
    Devout Follower Of He Who Walks Behind The Rows NightFlyer's Avatar
    Join Date
    Jul 2013
    Racine County, WI, USA
    Solenoid on a carb - is that for an electric choke?
    "You can never use too much anti-seize!"

    --Josh S.

  8. #8
    Torque converter load. For some reason Farrar's torque converter requires cracking the throttle plates open way further than the other three automatic owners I've helped (Del, Garen, and Jim). Leads to idle and shutoff issues. The idea is wire a retracting type solenoid into the Park/Neutral safety switch to crack the throttle plates in gear (stoplights for example).

    Farrar also has a Champion rebuilt carb, not a Bill rebuilt carb. He still has several unused vacuum barbs (capped) that I remove and plug. Also has bare steel linkages that I paint. Plus my carbs go through five consecutive soakings (carb solution, lacquer thinner, acetone, 91% alcohol, mineral spirits) -- they are nothing if not clean. Steve and Drew are running Bill carbs.

    Bill Robertson

  9. #9
    Uncensored Hypocrite stevedmc's Avatar
    Join Date
    Jul 2013
    Baton Rouge, LA
    Quote Originally Posted by content22207 View Post
    Farrar also has a Champion rebuilt carb, not a Bill rebuilt carb.

    Nope. Farrar is running a Steve carb. We rebuilt it about 18 months ago with an AutoZone kit.
    Rest assured, we have a backup of Farrar's car blog and it will be restored in the near future. (Steve Rice - March 2016)
    Rest assured, we have a backup of Shep's posts and all of them will be restored in the near future. (Steve Rice - March 2017)

  10. #10
    Capped off vacuum barbs are still there -- I saw them with my own eyes. Rusty linkages too.

    Did you all soak the carb? I tear mine down to bare metal and soak them for two weeks straight (bottom casting can't fit in my soaker at the same time with the top casting, choke housing, etc -- takes 10 days to do them all).

    Bill Robertson

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