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Thread: Carb problem

  1. #1

    Carb problem

    Here's the background information.

    Minnie is a 1963 Beech Musketeer, Model 23, S/N M-238.

    The engine is a Lycoming O-320-D2B, with approximately 3450 hours
    TT. It has been overhauled twice in the field and has approx 1120
    hours SMOH.

    The carb is a Marvel-Schebler Model MA-4-SPA, P/N 10-3678-32. The
    logs do not indicate it has ever been overhauled or replaced.

    The air filter element and all aero-duct under the cowl were
    replaced at the last annual, approx one year to the day and 100
    hours ago.

    Here's what happened.

    Thursday night, 2 June I flew for about an hour and everything was
    normal.

    Sunday, 5 June I went to fly and start up was normal. I taxied to
    the fuel pumps and put approximately 10 gallons in each tank to
    bring them up to the slots.

    I started the engine taxied to the departure end of runway 17 at 1L0
    and did a run-up and mag check at 1800 rpm (per the POH for the
    plane). On the left mag everything was normal, about 100 rpm drop.
    On the right mag the drop was about the same, maybe just a little
    more but nothing terribly unusual. Then the engine seemed to run a
    little rough. This engine seldom if ever fouls plugs but I leaned
    the mixture some and it smoothed out. When I put it to full rich
    for takeoff it seemed to get a little rough so I decided not to go.
    Taxied back to the hanger and put it inside and decided to run it
    again. This time when I would rev the engine to 1800 rpm or so at
    full rich it would vibrate so much it would shake the panel. If I
    would lean the mixture she would smooth out. Decided this was not
    good.

    Spoke to some folks who told me it sounded like either the float was
    sinking (possibly a hole in it) causing it to run rich or there was
    something stuck between the needle and jet not allowing the float
    and needle to close off the jet also causing it to run rich and
    rough. Suggested I try some high speed taxi to see if it cleared up.

    Monday, 6 June I went out and fired her up. Same thing. Ran OK at
    first. Mag check seemed OK at first then would run rough. If I
    leaned it would smooth out. Would have to pull the mixture knob out
    about two inches for it to smooth out. At the end of every run I
    would go to full rich, it would run rough. I'd lean and it would
    smooth out. With a 4,000 foot runway she was wanting to fly well
    before the end of the runway so I couldn't go the whole runway at
    full throttle, so I sat on the on the taxiway and ran it at full
    throttle for over a minute at full throttle and leaned it was
    smooth. After that if I'd go to full rich it would run rough again.

    Put her to bed and decided maybe it was time for a rebuilt carb. My
    A&P had written down all the data on the carb last annual so I had
    the info I needed to order it. I wanted to be sure I had the right
    data before ordering so I tried to read it myself. Could only see
    the data plate with a mirror and could read the model number but not
    the P/N. Decided I'd wait and decowl her and verify the data before
    ordering. (Didn't want to give Spruce $559 for the wrong carb and
    have a hassle with an exchange.)

    Sunday 12 June pulled the prop and cowl (have to pull the prop to
    decowl a `63 Mouse if you don't have the split cowl kit installed).
    I was copying the data off the plate and my neighbor, a Cessna 150
    driver that was giving me a hand, said why don't you take a look in
    the carb. I got a mirror and gave it to him while I went to get a
    flashlight. He said I see the problem.

    HE FOUND A MUD DOBBER NEST AND ONE WELL DONE TREE FROG ABOVE THE
    BUTTERFLY FOR THE CARB HEAT.

    So how did that cause the problem? They restricted the airflow
    enough to make the mixture too rich at full throttle, even maybe at
    half throttle.

    So how did they get in? The shroud for the carb heat wraps around
    the exhaust pipe between No. 3 cylinder and the muffler. It's open
    on both ends to let air (and mud dobbers and tree frogs) in. Then
    there's aero duct from the bottom of the carb heat shroud to the
    carb. Apparently the butterfly valve wasn't closing enough to keep
    them out of the carb. (I still have to check that closer).

    Problem solved, I HOPE. She's all back together but it was too hot
    to fly her by that time Sunday. I'll take her for a test drive
    tonight. She did run smooth at full throttle and full rich after
    the mud dobber and tree frog ectomy.

    I'll report back tomorrow.

    Cloyd Van Hook
    President, BAC





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  2. #2

    Carb problem

    Cloyd,
    It's a tough decision to NOT go, when the engine is running, you're
    sitting at the departure end of the runway and "it's just a stumble
    in one mag."

    Wise decision!

    Last year I took my brother flying in a Cessna 150. We had a pretty
    good time and the plane ran well. After tying down, we were
    standing by the nose and a mouse popped his head out of the scat
    tube that goes to the cabin or carb heat (don't remember which).
    He'd been with us for the whole flight!
    Bob

    --- In musketeermail@yahoogroups.com, "cloydvanhook"
    <cloydvanhook@i...> wrote:
    > Here's the background information.
    >
    > Minnie is a 1963 Beech Musketeer, Model 23, S/N M-238.
    >
    > The engine is a Lycoming O-320-D2B, with approximately 3450 hours
    > TT. It has been overhauled twice in the field and has approx 1120
    > hours SMOH.
    >
    > The carb is a Marvel-Schebler Model MA-4-SPA, P/N 10-3678-32. The
    > logs do not indicate it has ever been overhauled or replaced.
    >
    > The air filter element and all aero-duct under the cowl were
    > replaced at the last annual, approx one year to the day and 100
    > hours ago.
    >
    > Here's what happened.
    >
    > Thursday night, 2 June I flew for about an hour and everything was
    > normal.
    >
    > Sunday, 5 June I went to fly and start up was normal. I taxied to
    > the fuel pumps and put approximately 10 gallons in each tank to
    > bring them up to the slots.
    >
    > I started the engine taxied to the departure end of runway 17 at
    1L0
    > and did a run-up and mag check at 1800 rpm (per the POH for the
    > plane). On the left mag everything was normal, about 100 rpm
    drop.
    > On the right mag the drop was about the same, maybe just a little
    > more but nothing terribly unusual. Then the engine seemed to run
    a
    > little rough. This engine seldom if ever fouls plugs but I leaned
    > the mixture some and it smoothed out. When I put it to full rich
    > for takeoff it seemed to get a little rough so I decided not to
    go.
    > Taxied back to the hanger and put it inside and decided to run it
    > again. This time when I would rev the engine to 1800 rpm or so at
    > full rich it would vibrate so much it would shake the panel. If I
    > would lean the mixture she would smooth out. Decided this was not
    > good.
    >
    > Spoke to some folks who told me it sounded like either the float
    was
    > sinking (possibly a hole in it) causing it to run rich or there
    was
    > something stuck between the needle and jet not allowing the float
    > and needle to close off the jet also causing it to run rich and
    > rough. Suggested I try some high speed taxi to see if it cleared
    up.
    >
    > Monday, 6 June I went out and fired her up. Same thing. Ran OK
    at
    > first. Mag check seemed OK at first then would run rough. If I
    > leaned it would smooth out. Would have to pull the mixture knob
    out
    > about two inches for it to smooth out. At the end of every run I
    > would go to full rich, it would run rough. I'd lean and it would
    > smooth out. With a 4,000 foot runway she was wanting to fly well
    > before the end of the runway so I couldn't go the whole runway at
    > full throttle, so I sat on the on the taxiway and ran it at full
    > throttle for over a minute at full throttle and leaned it was
    > smooth. After that if I'd go to full rich it would run rough
    again.
    >
    > Put her to bed and decided maybe it was time for a rebuilt carb.
    My
    > A&P had written down all the data on the carb last annual so I had
    > the info I needed to order it. I wanted to be sure I had the
    right
    > data before ordering so I tried to read it myself. Could only see
    > the data plate with a mirror and could read the model number but
    not
    > the P/N. Decided I'd wait and decowl her and verify the data
    before
    > ordering. (Didn't want to give Spruce $559 for the wrong carb and
    > have a hassle with an exchange.)
    >
    > Sunday 12 June pulled the prop and cowl (have to pull the prop to
    > decowl a `63 Mouse if you don't have the split cowl kit
    installed).
    > I was copying the data off the plate and my neighbor, a Cessna 150
    > driver that was giving me a hand, said why don't you take a look
    in
    > the carb. I got a mirror and gave it to him while I went to get a
    > flashlight. He said I see the problem.
    >
    > HE FOUND A MUD DOBBER NEST AND ONE WELL DONE TREE FROG ABOVE THE
    > BUTTERFLY FOR THE CARB HEAT.
    >
    > So how did that cause the problem? They restricted the airflow
    > enough to make the mixture too rich at full throttle, even maybe
    at
    > half throttle.
    >
    > So how did they get in? The shroud for the carb heat wraps around
    > the exhaust pipe between No. 3 cylinder and the muffler. It's
    open
    > on both ends to let air (and mud dobbers and tree frogs) in. Then
    > there's aero duct from the bottom of the carb heat shroud to the
    > carb. Apparently the butterfly valve wasn't closing enough to
    keep
    > them out of the carb. (I still have to check that closer).
    >
    > Problem solved, I HOPE. She's all back together but it was too
    hot
    > to fly her by that time Sunday. I'll take her for a test drive
    > tonight. She did run smooth at full throttle and full rich after
    > the mud dobber and tree frog ectomy.
    >
    > I'll report back tomorrow.
    >
    > Cloyd Van Hook
    > President, BAC




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  3. #3

    Carb problem

    There has been at lest one AD, SB or BS regarding the carb on a 63.

    Suggest lookin into it s'more.

    jon

    --- In musketeermail@yahoogroups.com, "cloydvanhook"
    <cloydvanhook@i...> wrote:
    > Here's the background information.
    >
    > Minnie is a 1963 Beech Musketeer, Model 23, S/N M-238.
    >
    > The engine is a Lycoming O-320-D2B, with approximately 3450 hours
    > TT. It has been overhauled twice in the field and has approx 1120
    > hours SMOH.
    >
    > The carb is a Marvel-Schebler Model MA-4-SPA, P/N 10-3678-32. The
    > logs do not indicate it has ever been overhauled or replaced.
    >
    > The air filter element and all aero-duct under the cowl were
    > replaced at the last annual, approx one year to the day and 100
    > hours ago.
    >
    > Here's what happened.
    >
    > Thursday night, 2 June I flew for about an hour and everything was
    > normal.
    >
    > Sunday, 5 June I went to fly and start up was normal. I taxied to
    > the fuel pumps and put approximately 10 gallons in each tank to
    > bring them up to the slots.
    >
    > I started the engine taxied to the departure end of runway 17 at 1L0
    > and did a run-up and mag check at 1800 rpm (per the POH for the
    > plane). On the left mag everything was normal, about 100 rpm drop.
    > On the right mag the drop was about the same, maybe just a little
    > more but nothing terribly unusual. Then the engine seemed to run a
    > little rough. This engine seldom if ever fouls plugs but I leaned
    > the mixture some and it smoothed out. When I put it to full rich
    > for takeoff it seemed to get a little rough so I decided not to go.
    > Taxied back to the hanger and put it inside and decided to run it
    > again. This time when I would rev the engine to 1800 rpm or so at
    > full rich it would vibrate so much it would shake the panel. If I
    > would lean the mixture she would smooth out. Decided this was not
    > good.
    >
    > Spoke to some folks who told me it sounded like either the float was
    > sinking (possibly a hole in it) causing it to run rich or there was
    > something stuck between the needle and jet not allowing the float
    > and needle to close off the jet also causing it to run rich and
    > rough. Suggested I try some high speed taxi to see if it cleared up.
    >
    > Monday, 6 June I went out and fired her up. Same thing. Ran OK at
    > first. Mag check seemed OK at first then would run rough. If I
    > leaned it would smooth out. Would have to pull the mixture knob out
    > about two inches for it to smooth out. At the end of every run I
    > would go to full rich, it would run rough. I'd lean and it would
    > smooth out. With a 4,000 foot runway she was wanting to fly well
    > before the end of the runway so I couldn't go the whole runway at
    > full throttle, so I sat on the on the taxiway and ran it at full
    > throttle for over a minute at full throttle and leaned it was
    > smooth. After that if I'd go to full rich it would run rough again.
    >
    > Put her to bed and decided maybe it was time for a rebuilt carb. My
    > A&P had written down all the data on the carb last annual so I had
    > the info I needed to order it. I wanted to be sure I had the right
    > data before ordering so I tried to read it myself. Could only see
    > the data plate with a mirror and could read the model number but not
    > the P/N. Decided I'd wait and decowl her and verify the data before
    > ordering. (Didn't want to give Spruce $559 for the wrong carb and
    > have a hassle with an exchange.)
    >
    > Sunday 12 June pulled the prop and cowl (have to pull the prop to
    > decowl a `63 Mouse if you don't have the split cowl kit installed).
    > I was copying the data off the plate and my neighbor, a Cessna 150
    > driver that was giving me a hand, said why don't you take a look in
    > the carb. I got a mirror and gave it to him while I went to get a
    > flashlight. He said I see the problem.
    >
    > HE FOUND A MUD DOBBER NEST AND ONE WELL DONE TREE FROG ABOVE THE
    > BUTTERFLY FOR THE CARB HEAT.
    >
    > So how did that cause the problem? They restricted the airflow
    > enough to make the mixture too rich at full throttle, even maybe at
    > half throttle.
    >
    > So how did they get in? The shroud for the carb heat wraps around
    > the exhaust pipe between No. 3 cylinder and the muffler. It's open
    > on both ends to let air (and mud dobbers and tree frogs) in. Then
    > there's aero duct from the bottom of the carb heat shroud to the
    > carb. Apparently the butterfly valve wasn't closing enough to keep
    > them out of the carb. (I still have to check that closer).
    >
    > Problem solved, I HOPE. She's all back together but it was too hot
    > to fly her by that time Sunday. I'll take her for a test drive
    > tonight. She did run smooth at full throttle and full rich after
    > the mud dobber and tree frog ectomy.
    >
    > I'll report back tomorrow.
    >
    > Cloyd Van Hook
    > President, BAC







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    www.beechaeroclub.org


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