Announcement

Collapse
No announcement yet.

Flat spot in throttling......

Collapse
X
 
  • Filter
  • Time
  • Show
Clear All
new posts

    #16
    Is it a Holley carb? Was it rebuilt with automotive kit instead of marine?! The two use different power valves and that may be the issue. Doubt fuel pressure since idle and high speed are fine.
    Tony Bacon,
    Washougal, WA
    Caspian
    1997 3788 Twin Cummins 250hp

    Comment


      #17
      I will venture its a mercarb.....and it has the drain port back to the fuel source.

      Comment


      • builderdude
        builderdude commented
        Editing a comment
        Post a pic of it

      #18
      OK.... I will get a picture when the rain....stops, at least its not thunder and lightning I did start it up, been setting a week. It started instantly, choke plate closed, very rich and slight blue smoke, sort of stumbling/rough until it started to open, and I backed off the throttle as the RPM's rose, trying to keep her around 1500. She smoothed right out after maybe a minute......
      I decided to play with the throttle to see if I could get it duplicate the "flat spot".
      I could, if I gave it a quick shove forward, it would stumble, not miss or backfire, just a dead spot, right at the beginning of acceleration....
      If I "eased" it up, she responds fine, no stumble, or flat spot.....

      Is this a clue?

      Comment


      • builderdude
        builderdude commented
        Editing a comment
        Post 12

      • Bacon
        Bacon commented
        Editing a comment
        I am assuming that by "eased up" you mean advance the throttle more slowly. If so then on your description alone the accelerator pump is suspect. The purpose of this thing is to make up for the fact that fuel is denser than air. When the throttle is opened quickly the air increases faster that the fuel resulting in a momentary lean mixture. The pump simply squirts some fuel in for an instant to make up for the lag in fuel delivery. When the throttle is opened slowly the fuel does not lag behind the air as dramatically and the momentary lean mixture is avoided.
        Last edited by Bacon; 09-09-2019, 08:42 PM. Reason: completeness

      #19
      Yes, that is exactly what I mean.....now what, pull the carb, or try and test it. I read you warm it up, shut it down, then pull arrestor, and with motor off, pump the carb manually, looking for a good stream of fuel into the bowl/horn.....what is a good stream tho?
      I kinda remember when I rebuilt the original one, that I have still SOMEWHERE....arg, that the pump was that round hex part on the carb, is that right, and it has to move freely, with a clicking noise?

      Comment


      • builderdude
        builderdude commented
        Editing a comment
        Pic of carb?

      #20
      Ok...OK.....I did, and I am glad I did......

      I left the drain plug in from last out, that would have been on Sunday, day before Labor Day.....
      And we had LOTS of rain Saturday night, showers everyday since....
      And I had water under the engine. Turned on the bilge and she pumper for a spell....oops.
      I nosed her up a little more, and took out the plug.....

      To the carb. I fired her up, warmed her up, then shut her down. Pulled the arrestor and noticed the valve was not open all the way.....just a tad over 45 degrees maybe.
      Since it was warm, I loosened the three screws on the choke and spun her till it opened the vale all the way, then screwed them tight.

      I fired it back up, no stumble, she responds the way I would THINK it should.
      So, what, I wait till she cools, then see how well she "chokes" and starts?

      Oh yeah, pictures......The one with me choking in my speedos....didn't come out to good, hope these others help







      Comment


        #21
        Yep, see how she starts after sitting overnight.
        Dave
        Edmonds, WA
        "THE FIX"
        '93 2556 5.7 Bravo II 2.0:1 18 1/4x19 P
        (.030 over-Vortec top end-part closed cooled)
        The rebuild of my 2556 https://www.baylinerownersclub.org/f...76?view=thread
        Misc. projects thread
        https://www.baylinerownersclub.org/f...56-gctid789773

        Comment


          #22
          Ok.....the motor was as cold as the wifes heart, after I informed her my tip, I had in the 5th race at Churchill Down, that I put my paycheck on.... wasn't such a good tip, after all

          She fired the BEST it ever has......no rough idling or "over" choking/rich. She was smooth, and sweet....heck, I was surprised, it was like cast off and go!

          I didn't look at positioning of the valve, as it is all buttoned up still, I thought I would just try it first, then look if I needed too.....

          I couldn't get it to stumble, she advanced evenly and smooth, from a quick push on the throttle (from idle) to @ 2000 RPM, and the same with a slow even acceleration on the stick.

          I guess I fixed it?

          I am hoping for a few more trips out to get silvers, after I get back from the Columbia River trip, leaving tomorrow with the trailer, before I put her to bed.....not sure if a "load" will make any difference, we'll see.

          THANKS ALL!

          Comment


          • Bacon
            Bacon commented
            Editing a comment
            Nice! Yup, stick a fork in it it's done. Not literally down through the carb though. 😀

          #23
          Hopefully it was just a simple choke issue.
          Have a safe trip to the Columbia.
          I too am hoping for a few more silvers in our area but seems to be slowing now.
          Dave
          Edmonds, WA
          "THE FIX"
          '93 2556 5.7 Bravo II 2.0:1 18 1/4x19 P
          (.030 over-Vortec top end-part closed cooled)
          The rebuild of my 2556 https://www.baylinerownersclub.org/f...76?view=thread
          Misc. projects thread
          https://www.baylinerownersclub.org/f...56-gctid789773

          Comment


            #24
            If you look at the fish counts out in the straights, the main body of fish have yet to arrive, I believe, look for a good snap later this month

            Comment

            Working...
            X