4055 transition from idle

Discussion in 'Carter' started by FormerGNowner, Sep 13, 2016.

  1. FormerGNowner

    FormerGNowner Well-Known Member

    Got the carb back from National Carb in Florida and am generally happy with the rebuild, Except...it's very difficult to come off of idle smoothly. I wouldn't call it a hesitation, more like an unnecessarily harsh transition away from the idle circuit. The throttle linkage seems smooth - where should I start once the air cleaner is removed?


    DEADMANSCURVE my first word : truck

    sure , i'll make a guess i suppose . that's a 4bbl carter carb - carb #4055 ?
    since no disassmbly is involved with this i would maybe pop off the 2 metering rod covers ( SMALL SCREWS - CAREFUL ) and pull those out and inspect . there should be two long skinny springs under the pistons and a small diameter "pig tail" spring around top of piston holdig rod top in place . pay close attention to orientation of rod top springs . make sure the rods are straight and the ends taper down correctly . when you put them back in they may not slip right down into the front jets without a little up n down ( carefully ! ) massaging . when lined up they will slide into place and you will be able to replace covers . also unhook the pump lever and move pump rod up n down a little to make sure that feels "springy" enough with more resistance as you get to the down position as the rubber rubs against the housing wall .
    i think some rebuilders assemble the rods into the cover assembly first ( easy ) then try and install top . easy to bend rods that way ( been there , done that ) . also note the small numbers stamped into the metering rods , about midway down shaft .
    if that is no help then you'll have to pull the lid and check 'er over .
    edit : grabbed my carter book at lunch . #4055 = 1966 buick 340 automatic ( service carb #4331 ) . correct ?
    Last edited: Sep 16, 2016
  3. FormerGNowner

    FormerGNowner Well-Known Member

    edit : grabbed my carter book at lunch . #4055 = 1966 buick 340 automatic ( service carb #4331 ) . correct ? Lots of unknown history here. The car was originally a 300-2V automatic. It's now a 4bbl-4speed. I'm fairly sure that the 4055S carb and intake came off an automatic car since it still has the dashpot to dampen the return of the throttle linkage.

    The rods (16-7057, close to stock) and pistons seem to move OK, as well as the pump. Would going to a different hole on the pump linkage affect this?


    DEADMANSCURVE my first word : truck

    maybe ?
    I usually set them up using the middle hole ( on a 3 hole arm ) as a start up point .
    the lower hole will give you less pump shot at a slower rate , the upper hole will give you more quicker . geometry .
  5. FormerGNowner

    FormerGNowner Well-Known Member

    Thanks DM. National installed a 3/4" diameter pump; the parts list from Mike's Carb shows 11/16" for this carb. I'm going to assume that the current pump is too tight in the bore and doesn't start its motion smoothly. Waiting on a new part to see if I'm right.


    DEADMANSCURVE my first word : truck

    worth a try I guess . I would think that too loose would maybe have more of a chance to cause your problems . but still , easy enough to check .
    and food for thought - the edelbrock 600's and the 750's take a dif pump piston . so maybe the 750 version is bigger in diameter to fit down a larger diameter hole = more volume ? I think I have one of each , if so i'll try and measure both and see .
    edit : well finally got a chance to check . no big dif . 600 carb pump is .820 across rubber , 750 carb pump is .830 across rubber . and that's trying to measure across a soft surface so ----- ? and did not see much eyeball dif in height , spring etc .
    Last edited: Sep 28, 2016

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