| Tuning
the Bing 64 altitude compensating carburetor
This procedure was taken
from Ultralight News. Its author is unknown. FlyDivers has made a few
small changes for clarity and to make the procedures generic,
regardless of engine.
Required tools:
A feeler
gauge.
A double vacuum gauge.
Two 9 mm open end wrenches to adjust the M5 nuts on the throttle
cables.
The following are the recommended steps to adjust the carburetors.
IMPORTANT: make sure cables
are not effected by ANY engine movement, and that they move
FREELY back and forth with no stickiness. It is also advisable to make
all of the cables and housings that lead from a cable splitter to the
carburetors the same length. This eliminates the possibility of
differing bend radii tensioning at different rates as tension is
applied to the cables. If one intake manifold supplies more fuel
mixture, and as a direct result more power output than another,
moderate to severe vibration will be induced. It is therefore critical
that carburetors on multi carburetor engines be carefully balanced.
CAUTION: Ensure that your
aircraft is immobilized by tying it to an immovable object. Wheel
chocks and similar barriers are NOT sufficient.
- First step is to
- Make sure that the engine
has been loaded with a properly adjusted propeller that limits the rpm
tied down on the ground to the maximum static rpm recommended
by the engine manufacturer.
- Make sure that both
throttle cables are allowing full opening of the throttle valve. This
can be done visually with the engine turned off and full power applied.
Also ensure that the cables are long enough to ensure that the throttle
actuators will go all the way closed. This should be done with the idle
screws all the way out counter clockwise.
- With the engine turned
off bring the throttle back to an idle. Adjust the idle screws counter
clockwise until the throttle actuating arm is against the
carburetor body.
- Adjust the idle screws in
until they just touch the actuating arms. Check to ensure the throttle
cables are long enough to allow full closure of the throttle actuator.
Now adjust the idle screws clockwise 1 1/2 turns.
- Gently adjust the air
mixture screws (air bleed screws) in all the way and then back them out
1 1/2 turns.
- Have someone start
applying throttle very slowly, Pre-adjust the cables at the fittings so
both cables begin opening the throttle arms at the same time.
- Start the engine and
allow it to come up to the recommended EGT and oil or water temperature
for your engine.
- Adjust the idle screws
equally until you obtain the engine manufacturer's recommended idle
speed.
- This procedure will
normally synchronize the carburetors at an idle.
- Adjust the idle mixture
using the air mixture screws (air bleed) for best idle. Move each screw
no more than 1/4 turn and wait for the engine to stabilize at the new
mixture setting.
- When best idle is
achieved on both carburetors, readjust both idle speed screws equally
to reset idle speed to recommended rpm.
- Once you have done this
bring the throttle to half throttle and measure the distance between
the throttle activation arm and the carburetor body, they should be the
same. This measurement should
be done throughout midrange to ensure that the measurement is the same
for both carburetors at all settings of the throttle. Note: Different engines will show vibration at
somewhat different rpm, however, if the vibration is due to unbalanced
throttle actuator cables, the vibration will normally show up early in
the midrange as the throttle actuator just begins to move into
midrange. Some mechanics advise leaving a small bit of slack (1/16") at
idle so that changes in temperature and adjustments at midrange
settings cannot affect cable tension at idle. Others prefer the cables
to be adjusted to remove the slack at idle. FlyDiver prefers a small
bit of slack because we will be fine tuning the cable adjustments in
midrange and that may affect idle.
- Advance to full throttle,
both throttle arms should be in the full open position and the engine
should achieve full power. Be certain to set the pitch on your
propeller to limit the maximum rpm to that recommended by the engine
manufacturer.
If there is a problem with
the synchronization of the cables it can usually be traced to movement in the outer throttle
casing. That is when you are applying throttle instead of it moving the
cable the outer casing is flexing or bending.
If this is the case you MUST
secure, or route the cable so that all of the throttle movement is
directed to the throttle arm. Again, making the cables and housings are
the same length greatly reduces differences in throttle movement caused
by the cables.
In the standard
configuration you would use #60 and & #58 to adjust the
throttle and choke set up with Bing carburetors.
Using a vacuum gauge
- First perform a manual
synchronization adjusting the Bowden cables so there is full travel
from full open to full closed of the throttle valve arm, as described
above.
- Then remove the
compensator tubes and install the gauges. Look for a small plug screw,
left of the idle mixture control screw on the carburetor. Ensure that
the plug screw is securely fastened
- After you adjust the
carburetors, the vacuum gauges should read the same at all engine
settings.
- Mercury column gauges are
also made that will do the same job as the vacuum gauges.
Remember, it's the
length and the tightness of the cables that adjusts the carburetor
synchronization in midrange. When you're adjusting them, you're simply
lengthening or shortening a cable, and making each throttle valve arm
move the same distance at the same time.
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