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Balking Motorhome

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  • Duane
    I just put a re-built carb on my 440-3 Executive MH. It purrs like a kitten while idling, but when I put it gear it balks-misses-backfires until I get the
    Message 1 of 6 , May 4, 2005
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      I just put a re-built carb on my 440-3 Executive MH. It purrs like a
      kitten while idling, but when I put it gear it balks-misses-backfires
      until I get the revs up. I checked for vacuum leaks etc. to no
      avail. What can be the matter?

      Dad
    • davidkerryedwards
      I had a similar problem when the idle speed adjustment was keeping the idle up, but the idle adjusting screws were too tight. If it s a Holley carb, there
      Message 2 of 6 , May 4, 2005
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        I had a similar problem when the idle speed adjustment was keeping the
        idle up, but the idle adjusting screws were too tight. If it's a
        Holley carb, there should be one idle adjustment screw on each side of
        the secondary bowl. On mine, (1971 413) the basic adjustment is one
        turn out. Try a little further out and see if it solves your problem.

        Kerry

        --- In classicrv@yahoogroups.com, "Duane" <deschwar@h...> wrote:
        > I just put a re-built carb on my 440-3 Executive MH. It purrs like a
        > kitten while idling, but when I put it gear it balks-misses-backfires
        > until I get the revs up. I checked for vacuum leaks etc. to no
        > avail. What can be the matter?
        >
        > Dad
      • Jack Rabon
        Sounds like an idle mixture problem to me, too. Exactly the same symptoms you see in an aircraft which is leaned out for long idle & taxi times. Aircraft
        Message 3 of 6 , May 5, 2005
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          Sounds like an idle mixture problem to me, too.

          Exactly the same symptoms you see in an aircraft which is "leaned out" for
          long idle & taxi times. Aircraft engines often gunk up their spark plugs
          when idled for a long time, so pilots are taught to pull the mixture
          control back to really thin the mixture.

          But asking for full power with a leaned mixture is likely to result in
          engine damage (if you forget to go to full rich on takeoff). So the right
          way to do it is to lean a lot. The engine runs at idle quite happily, and
          can even run just a tad above idle quite well. But it balks and falls flat
          when the throttle is advanced more. Kinda like you described.

          If your carb has not been touched, you might have some foreign material in
          the idle circuit. Sometimes going to real rich on the idle screws will let
          the tiny gunk pass the needle. Or you might have to clean the carb.

          I would open one side idle mixture screw a lot, while the engine is at
          idle. Then close it all the way & open to the suggested setting. Then do
          the other side. Often the engine will die when you close the screw for the
          initial setting.

          It should run at the suggested initial setting. Then adjust for best idle
          speed, unless you have an exhaust gas analyzer available for real good
          settings.

          If the idle speed goes up too much, set the engine back to the correct idle
          (650 rpm from memory?) and readjust the idle screws. Go slow and wait for
          each adjustment step to take effect. That four barrel intake manifold
          takes several cylinder fillings at idle to go to the new mixture setting
          when you move the screw a bit.

          So relax, and enjoy the sound of a 7.2 liter engine at idle as you make the
          changes.

          Jack

          -----Original Message-----
          Date: Wed, 04 May 2005 21:14:29 -0000
          From: "Duane" <deschwar@...>
          Subject: Balking Motorhome

          I just put a re-built carb on my 440-3 Executive MH. It purrs like a
          kitten while idling, but when I put it gear it balks-misses-backfires
          until I get the revs up. I checked for vacuum leaks etc. to no
          avail. What can be the matter?

          Dad
        • Duane
          I have messed around with the idle screws can t remember is turning in leaning and out enriching? Dad ... out for ... spark plugs ... mixture ... result in
          Message 4 of 6 , May 5, 2005
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            I have messed around with the idle screws can't remember is turning
            in leaning and out enriching?
            Dad






            --- In classicrv@yahoogroups.com, Jack Rabon <rabonj@b...> wrote:
            > Sounds like an idle mixture problem to me, too.
            >
            > Exactly the same symptoms you see in an aircraft which is "leaned
            out" for
            > long idle & taxi times. Aircraft engines often gunk up their
            spark plugs
            > when idled for a long time, so pilots are taught to pull the
            mixture
            > control back to really thin the mixture.
            >
            > But asking for full power with a leaned mixture is likely to
            result in
            > engine damage (if you forget to go to full rich on takeoff). So
            the right
            > way to do it is to lean a lot. The engine runs at idle quite
            happily, and
            > can even run just a tad above idle quite well. But it balks and
            falls flat
            > when the throttle is advanced more. Kinda like you described.
            >
            > If your carb has not been touched, you might have some foreign
            material in
            > the idle circuit. Sometimes going to real rich on the idle screws
            will let
            > the tiny gunk pass the needle. Or you might have to clean the
            carb.
            >
            > I would open one side idle mixture screw a lot, while the engine
            is at
            > idle. Then close it all the way & open to the suggested setting.
            Then do
            > the other side. Often the engine will die when you close the
            screw for the
            > initial setting.
            >
            > It should run at the suggested initial setting. Then adjust for
            best idle
            > speed, unless you have an exhaust gas analyzer available for real
            good
            > settings.
            >
            > If the idle speed goes up too much, set the engine back to the
            correct idle
            > (650 rpm from memory?) and readjust the idle screws. Go slow and
            wait for
            > each adjustment step to take effect. That four barrel intake
            manifold
            > takes several cylinder fillings at idle to go to the new mixture
            setting
            > when you move the screw a bit.
            >
            > So relax, and enjoy the sound of a 7.2 liter engine at idle as you
            make the
            > changes.
            >
            > Jack
            >
            > -----Original Message-----
            > Date: Wed, 04 May 2005 21:14:29 -0000
            > From: "Duane" <deschwar@h...>
            > Subject: Balking Motorhome
            >
            > I just put a re-built carb on my 440-3 Executive MH. It purrs
            like a
            > kitten while idling, but when I put it gear it balks-misses-
            backfires
            > until I get the revs up. I checked for vacuum leaks etc. to no
            > avail. What can be the matter?
            >
            > Dad
          • Mark
            Dad, Out is rich, in is lean. Can t speak for your particular model, but a rule of thumb for most carbs mixture screws is 1 to 1 1/2 turns out from closed,
            Message 5 of 6 , May 5, 2005
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              Dad,

              Out is rich, in is lean. Can't speak for your particular model, but a rule of thumb for most carbs mixture screws is 1 to 1 1/2 turns out from closed, but closed means with your fingers, NOT with a screwdriver. There's a fine point on the hidden end of the screw. If it gets shoved into the hole too hard, it can deform and you'll lose the fine tune ability.

              With the engine warm and idling, screw one in a little and wait a few seconds to see if there's a change. When it slows down a bit, back it out (slowly) until it stumbles again...put the screw right in the middle, then do the other side. Recheck the first one and reset your idle speed if needed. That oughta rough you in for carb adjustment.

              Be sure the vacuum lines to your distributor are correct...your problem could come from over advanced timing at idle, if your vacuum controlled dashpot isn't pulling it back.

              Mark in Modesto

              [Non-text portions of this message have been removed]
            • Duane
              Many thanks Mark Dad ... a rule of thumb for most carbs mixture screws is 1 to 1 1/2 turns out from closed, but closed means with your fingers, NOT with a
              Message 6 of 6 , May 6, 2005
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                Many thanks Mark

                Dad





                --- In classicrv@yahoogroups.com, "Mark" <mark@J...> wrote:
                > Dad,
                >
                > Out is rich, in is lean. Can't speak for your particular model, but
                a rule of thumb for most carbs mixture screws is 1 to 1 1/2 turns out
                from closed, but closed means with your fingers, NOT with a
                screwdriver. There's a fine point on the hidden end of the screw. If
                it gets shoved into the hole too hard, it can deform and you'll lose
                the fine tune ability.
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