Surging

Discussion in 'Mopar Performance Issues' started by moparmucelli, Jun 22, 2018.

  1. moparmucelli

    moparmucelli Well-Known Member

    Messages:
    114
    Likes Received:
    2
    Joined:
    Sep 15, 2013
    Location:
    murrieta ca
    Local Time:
    1:57 PM
    hi guys I had a problem with surging a while back and I got a lot of input on it and I was messing around with the vacuum advance I had it in manifold vacuum and I plugged it into portal vacuum and it seems to run better why is that?
     
  2. Caliscamp72

    Caliscamp72 Mostly sane GM Destroyer FABO Gold Member

    Messages:
    71
    Likes Received:
    26
    Joined:
    May 17, 2016
    Location:
    Vista Calif.
    View My Photos
    Local Time:
    1:57 PM
    Manifold vacuum sources allow vacuum to advance at idle with throttle plates closed AND as they open .
    Ported vacuum sources give no vaccum signal at idle with plates closed and only after they open enuff to expose the "port" .
     
  3. Caliscamp72

    Caliscamp72 Mostly sane GM Destroyer FABO Gold Member

    Messages:
    71
    Likes Received:
    26
    Joined:
    May 17, 2016
    Location:
    Vista Calif.
    View My Photos
    Local Time:
    1:57 PM
    Manifold vacuum would be giving you full VAC advance at idle . Part throttle cruise is mainly where vac advance "works" by design.
     
  4. moparmucelli

    moparmucelli Well-Known Member

    Messages:
    114
    Likes Received:
    2
    Joined:
    Sep 15, 2013
    Location:
    murrieta ca
    Local Time:
    1:57 PM
    Oh ok I see but why was my car surging with the manifold vacuum?
     
  5. RustyRatRod

    RustyRatRod Just another dumbass. FABO Gold Member Technical Editor

    Messages:
    45,475
    Likes Received:
    9432
    Joined:
    Jun 7, 2010
    Location:
    Georgia
    View My Photos
    Local Time:
    4:57 PM
    It was probably pulling too much timing in with manifold vacuum. You need to re-adjust the timing since you changed to the ported vacuum side.
     
  6. BigBlockMopar

    BigBlockMopar BigBlockMember

    Messages:
    1,381
    Likes Received:
    356
    Joined:
    May 1, 2011
    Location:
    Netherlands
    Local Time:
    10:57 PM
    Ported vacuum possibly hides the issue.
    *Usually* surging is a lack of fuel.
     
    • Like Like x 1
    • Caliscamp72

      Caliscamp72 Mostly sane GM Destroyer FABO Gold Member

      Messages:
      71
      Likes Received:
      26
      Joined:
      May 17, 2016
      Location:
      Vista Calif.
      View My Photos
      Local Time:
      1:57 PM
      Was the engine surging at idle ? Like rpm hunting ..... Or are you saying it surged at cruise ? Like you physically feel an extra load coming and going while at speed ( as if you were lightly applying brakes or like when an air conditioner kicks on and off on a smaller engine)???
       
    • moparmucelli

      moparmucelli Well-Known Member

      Messages:
      114
      Likes Received:
      2
      Joined:
      Sep 15, 2013
      Location:
      murrieta ca
      Local Time:
      1:57 PM
      Only at cruising speeds
       
    • moparmucelli

      moparmucelli Well-Known Member

      Messages:
      114
      Likes Received:
      2
      Joined:
      Sep 15, 2013
      Location:
      murrieta ca
      Local Time:
      1:57 PM
      Yea rpm hunting
       
    • BigBlockMopar

      BigBlockMopar BigBlockMember

      Messages:
      1,381
      Likes Received:
      356
      Joined:
      May 1, 2011
      Location:
      Netherlands
      Local Time:
      10:57 PM
      Install an AFR gauge.
      Best tool for tuning a carb.
       
      • Like Like x 1
      • RustyRatRod

        RustyRatRod Just another dumbass. FABO Gold Member Technical Editor

        Messages:
        45,475
        Likes Received:
        9432
        Joined:
        Jun 7, 2010
        Location:
        Georgia
        View My Photos
        Local Time:
        4:57 PM
        Surging at highway speed with OBD cars is almost always a vacuum issue. No reason it would be any different for non computerized cars.
         
        • Agree Agree x 1
        • moparmucelli

          moparmucelli Well-Known Member

          Messages:
          114
          Likes Received:
          2
          Joined:
          Sep 15, 2013
          Location:
          murrieta ca
          Local Time:
          1:57 PM
          Ok I will look into it
           
        • 383Duster

          383Duster Well-Known Member

          Messages:
          1,540
          Likes Received:
          168
          Joined:
          Jan 11, 2009
          Location:
          Dallas, TX.
          Local Time:
          3:57 PM
          Blown carb gasket is possible..
           
        • moparmucelli

          moparmucelli Well-Known Member

          Messages:
          114
          Likes Received:
          2
          Joined:
          Sep 15, 2013
          Location:
          murrieta ca
          Local Time:
          1:57 PM
          Ok
           
        • crackedback

          crackedback FABO Gold Member FABO Gold Member

          Messages:
          17,759
          Likes Received:
          1690
          Joined:
          Aug 7, 2005
          Location:
          92201
          Local Time:
          1:57 PM
          Surging at cruise is usually too much timing or a lean condition.
           
        • moparmucelli

          moparmucelli Well-Known Member

          Messages:
          114
          Likes Received:
          2
          Joined:
          Sep 15, 2013
          Location:
          murrieta ca
          Local Time:
          1:57 PM
          Ok thanks
           
        • mcmlvii

          mcmlvii Active Member

          Messages:
          34
          Likes Received:
          0
          Joined:
          Feb 7, 2014
          Location:
          Poulsbo, Wash.
          Local Time:
          1:57 PM
          This was the problem I had, as my 383 car was surging at highway speeds and light throttle. I disconnected the vacuum advance and the problem went away, so I took the distributor apart and found the replacement vacuum canister I was using was marked 13 (distributor) degrees, so it was putting in 26 (crankshaft) degrees advance at high vacuum. The canister arm is sometimes (usually?) stamped with the degrees of distributor timing it will impose at high vacuum but you need to double that number to get "crankshaft" degrees - mine was stamped 13, thus 26 crankshaft degrees. I wrapped some wire around the canister arm to limit travel and it fixed the surge problem.
          20180606_150130.jpg

          The original vacuum canister on the car had a hole in the diaphragm but the arm was stamped 9.5, so it would put in 19 crankshaft degrees of timing at full vacuum. I didn't measure the timing advance after the wire modification but figure it is about in line with the original canister now.
          20180601_140603.jpg

          20180601_140641.jpg
           
        • AJ/FormS

          AJ/FormS 367 FormS clone 3.09-1.92-1.40-1.09-.78od 3.55s

          Messages:
          13,017
          Likes Received:
          2910
          Joined:
          Jan 19, 2014
          Location:
          South-Central Manitoba,Canada, 900ftelevation
          View My Photos
          Local Time:
          3:57 PM
          Once steady-state cruising, it shouldn't make a difference where the can is getting signal. At that point total available is total available.

          However I have seen some combos not pull the same vacuum from the two sources, and if the can was stiffly sprung, the two sources could be pulling different totals
           
          Last edited: Jun 30, 2018
        • halifaxhops

          halifaxhops I guess I have a gold member no one likes? FABO Gold Member

          Messages:
          42,025
          Likes Received:
          11303
          Joined:
          Jan 20, 2014
          Location:
          CENTRURAL, PA
          View My Photos
          Local Time:
          5:57 PM
          See if that vac canister is adjustable with a 3/32 allen wrench