Disassembling Your Bing Carburetor by Chris Wolf

Disassembling The Bing Carburetor

Recently I've been engaged in attempting to learn as much as possible about
my Bing 54 carburetor.  I've read all the articles in the CPS catalog, and
ordered and read the Tuning & Parts Manual from the Bing agency in Kansas.

Both the articles, and the manual, have a great deal of useful information
on how the carb works, and how to tune it.  But nowhere in any of this
information is there a detailed write-up on how to take the carb apart and
then re-assemble it.  There are exploded parts diagrams, to be sure, but
that's not the same thing as having a detailed write-up.  And there are
some aspects of carb disassembly that can be positively baffling if you've
never done it before.

The Bing people recommend that every Bing carb owner open the carb up and
at least check to see that it is properly jetted.  However I'll bet that a
very large percentage of PPC pilots have never done this, simply because
they don't know to take the carb apart and put it back together, and are
afraid to do so, lest they screw something up.  I'll bet the carb was
originally set by the dealer, and has never been touched since.  (That was
certainly the situation in my case.)

However there's no reason for this, since it's actually quite easy to open
the carb up, and check your jets (and all the rest of the parts).  And
since the Bing people also recommend that the carb be rebuilt every 100
hours, it seems to me that every PPC pilot should know how to open up his
carb, check it out, and then put it back together again.

I've documented this procedure for my own use, and I think it would be a
useful thing to pass on to the rest of the PPC pilots.  Certainly in all
the years I've been compiling information on PPC engines, I've never seen
this done anywhere.

So here is my documentation on how to take the Bing 54 carb apart, and put
it back together, and how to check and adjust the jets.  It's written from
the point of view of a complete novice (which is what I was, until very
recently).  I won't guarantee that my write-up is 100% accurate, but it is
as accurate as I can make it at my current level of knowledge.  If there
are any errors, please let me know so that I can correct them.  Depending
on how old your carbs are, how many you have, and what sort of air filter
you have, your setup may not exactly match mine, but it should be pretty
close.  I have a 503 Rotax engine, with a single Bing 54 carburetor.

So with that caveat, let's get started:

First, let's remove the carburetor from the plane.  It's a lot easier for a
novice to delve into the guts of the carb, if he's not squatting next to
the engine, peering up into the carb with a flashlight.

First, disconnect the fuel line that runs into the side of the carb.
Rather than struggling with the fuel line, trying to twist it off the
little metal nipple in the side of the carb, I just cut the line off and
replace it later.  Fuel line is very cheap, and easy to replace.  Why
struggle just to save a few pennies?

There are two cables running into the top of the carburetor; the throttle
control, and the choke control.  The choke control is on the right, while
the throttle control is in center of the top of the carb.  The choke
control is a brass fitting, about an inch long, with a hex nut base and a
skinny rubber boot on the top.  There's no need to remove the rubber boot.
Just use a wrench to unscrew the brass fitting where it screws into the
metal body of the carb.  Once the fitting is unscrewed, lift the entire
choke control assembly out of the body of the carb.  You should see a
little piston, about half an inch long, on the end of the fitting, with a
powerful spring behind it, trying to push it out of the body of the brass
fitting.  Leave this choke control assembly attached to the choke cable,
and set it aside.

Now let's remove the throttle cable from the top of the carb.  First we
must remove the lid of the carb.  There are two screws holding the lid on.
Unscrew them, but don't try to remove them from the lid.  They are designed
to stay with the lid. 

Gently lift the lid of the carb.  The first thing you will see is the top
of a large spring, about as big around as your thumb.  After about two
inches of this spring has emerged from the top of the carb, the throttle
valve piston will start to emerge.  This is a big metal piston, about an
inch and a half in diameter and about two inches long.  The piston is a
smooth slide fit inside the metal body of the carb.

As we continue to lift the carb lid, we see a tapering metal spike, about
two inches long, hanging from the bottom of the throttle valve piston.
This spike is called the JET NEEDLE, and it's primarily responsible for
regulating the fuel flow in the mid-range engine speeds from about
one-fourth throttle to about three-fourths throttle.

With the throttle valve piston assembly out of the way, let's take a moment
and peer down into the top of the carb.  What do we see?  In the bottom of
the carb, in the center, we see the top of a little cylinder, about a
quarter inch in diameter, with a hole in it.  This cylinder is the NEEDLE
JET.  As you may have guessed, the JET NEEDLE that we just removed, fits
down inside the opening of the NEEDLE JET.  The JET NEEDLE and the NEEDLE
JET work together, as a team, to regulate the amount of fuel that is fed to
the engine.  If you look closely at the JET NEEDLE, you'll see that it's
tapered.  Obviously if the JET NEEDLE is lowered into the opening of the
NEEDLE JET, the increasing taper of the needle gradually fills the opening
of the NEEDLE JET, and reduces the fuel flow.  Or if the JET NEEDLE is
raised out of the opening of the NEEDLE JET, the decreasing taper of the
needle gradually increases the opening in the NEEDLE JET, and increases the
fuel flow.  Congratulations!  You have just mastered the workings of the
most complicated part of the Bing 54 carburetor; the NEEDLE JET/JET NEEDLE

By the way, if you're having trouble keeping the difference between the JET
NEEDLE and the NEEDLE JET clear, just look at the last word of either part,
and it will tell you what we are talking about; the needle or the jet.  In
other words, the NEEDLE JET is the jet at the bottom of the carb, and the
JET NEEDLE is the long, tapering needle that is lowered into the NEEDLE
JET.  Go back and read this section a couple of times, if necessary, until
the difference between the NEEDLE JET and the JET NEEDLE is perfectly
clear.  It's really pretty simple, but it's easy to get the two mixed up
when you're just getting started.

What else do we see when we look down into the carburetor?  Well, there's a
big hole, about the size of a walnut, on opposite sides of the carb wall.
One hole goes out to the air filter, and the other hole goes into the
engine.  This passageway is called the VENTURI.  It's where the fuel
actually gets injected into the incoming airstream.

What else do we see inside the carb?  Where there's a big screw, about a
quarter inch in diameter, with a tapered point, coming through the side of
the carb.  This is the IDLE SPEED ADJUSTMENT SCREW, and it's used to adjust
the idle speed of the engine.

There are a couple of other holes that are visible in the bottom of the
carb.  These holes basically squirt gas into the carburetor under various
conditions, but we will ignore them for the moment.

Before we delve deeper in the body of the carb, let's take a closer look at
the piston assembly that we just removed from the carb.

The JET NEEDLE, hanging down from the body of the piston, comes in several
sizes and tapers.  If your engine is not running smoothly, it can sometimes
help to change to a different size needle.  However, before you can change
the needle, you need to be able to get it out of the piston.  To take the
piston assembly apart is incredibly difficult if you don't know the secret,
but incredibly easy if you do.

The secret is to remove the spring first.  How can you possibly get the
spring off of the throttle cable when it's being held at both ends by the
carb lid on one end, and the throttle valve piston on the other?

Simple!  Unscrew the spring!  Go to the very end of the spring, near the
lid, and force the throttle cable between the very end of the spring, and
the next coil of the spring.  Then start rotating the spring.  It will
quickly "unscrew" itself from the throttle cable.  Voila!  Now with that
damned spring out of the way, you can easily disassemble the remainder of
the piston assembly.

Look at the bottom of the piston.  Right next to the JET NEEDLE, you will
see a little white nubbin sticking out of a hole.  This nubbin is part of
the SPRING CUP that holds the lower end of the spring inside the piston.
Now that the spring is out of the way, take a bolt, screwdriver, or
toothpick, and push the nubbin back into the piston until the hole is

With the nubbin out of the way, you can free the throttle cable PIGTAIL
from the bottom of the piston.  The PIGTAIL is a little metal plug,
soldered to the end of the throttle cable.  The PIGTAIL anchors the
throttle cable to the bottom of the piston, so that when you pull on the
throttle cable, the PIGTAIL causes the piston to be lifted up, which pulls
the JET NEEDLE out of the NEEDLE JET, which allows more gasoline to flow
into the carb, which makes the engine run faster.  Starting to make sense?

The PIGTAIL sits in a little anchoring slot, right next to the hole that
was formerly occupied by the nubbin on the SPRING CUP.  In fact, the two
holes are connected by a slot.  Grab the lid of the carburetor and pull it
toward the piston.  This will give some slack to the throttle cable, and
should cause the PIGTAIL to slide out of its anchoring slot and flop around
freely.  Push the throttle cable up through the connecting slot, and into
the hole formerly occupied by the white nubbin on the SPRING CUP.  (It
helps if the hole is on the bottom, so that gravity assists you in getting
the cable into the hole, rather than fights you.

Once the throttle cable is in the hole, pull the piston and the carb lid
apart.  The PIGTAIL should slide out through the hole, and will be free of
the piston.  The white SPRING CUP should also slide out of the piston.  If
not, grab the spring cup with a pair of needle nose pliers, and slide it
out of the piston.

At this point, the throttle cable, with the PIGTAIL on the end, and the
white SPRING CUP should be removed from the piston.  The only thing still
left in the bottom of the piston is the JET NEEDLE.  Slide it out of the
piston.  Be careful. The JET NEEDLE assembly is kind of delicate.  Don't
bend it!

Set the piston aside, and let's take a closer look at the JET NEEDLE
assembly.  At the top of the JET NEEDLE is a little metal clip (called the
E CLIP) that snaps around a groove in the top of the JET NEEDLE.  In fact,
there are several grooves at the top of the JET NEEDLE.  Depending on how
old the needle is, there may be three, or four, grooves.

Moving the E CLIP up on the grooves, causes the engine to run leaner.
Moving the clip down on the grooves, causes the engine to run richer.  If
you're having trouble getting your engine to run at a constant speed in the
4500 to 5500 rpm range, it may be too rich, and moving the E CLIP up, one
or two notches, may cure the problem.  But if you move the E CLIP, keep an
eye on your EGT readings to make sure you haven't leaned the engine too

If you look closely at the E CLIP, you'll see that it has a break in the
metal, right next to the curved part of the clip that snaps around the body
of the JET NEEDLE.  This is as it should be.  Rest assured that you didn't
break the clip when you pulled the JET NEEDLE out of the piston.  (Of
course it never hurts to have a spare E CLIP, or two, around.)

The JET NEEDLE should have a tiny o-ring on it, about 3/16 inch in
diameter.  This o-ring should slide down over the top of the JET NEEDLE and
snug up against the E CLIP.  The purpose of this o-ring is to keep the JET
NEEDLE from spinning inside the E CLIP, and getting sawed in two.  If you
don't have one of these o-rings, order one from California Power Systems.
Part #963-505.  Don't fly without it!

We've seen everything there is to see on the top of the carburetor.  Now
let's remove the float bowl from the carb and explore the inner workings of
this amazing little gadget.  The first thing we need to do is remove the
carburetor from the engine.  Note that the carburetor is attached to the
engine by a short rubber flange, held on at each end by two screw clamps.
One clamp holds the flange to the intake manifold on the engine; the other
clamp holds the flange to the carburetor.  Use a screwdriver to loosen the
outer clamp holding the carburetor (no need to remove the inner clamp).
When the outer clamp has been loosened, you can pull the carburetor out of
the rubber flange.

Take the carburetor over to your workbench or table, and still holding it
upright (float bowl on the bottom) remove the float bowl from the bottom of
the carb.  The float bowl is held on by a heavy wire clip.  Simply rotate
the wire clip toward the air cleaner, and remove the float bowl from the
bottom of the carburetor by sliding it off.  Don't force it!  The float
bowl should slide off easily.

Inside the float bowl, you will see two small floats (and probably some
gasoline).  Remove the floats by sliding them up, off their vertical pins,
then dump out the gasoline.  Set the floats and float bowl aside, and let's
take a look at the guts of the carb.

Turn the carb upside down on your workbench, and prop up the air filter
side.  With the air cleaner to your left, you will see the MAIN JET
assembly in the center of the carb.  The MAIN JET is surrounded by a SIEVE
SLEEVE (it looks like a miniature fuel filter)  Just to the left of the
MAIN JET is a twin-arm brass assembly.  This is called the FLOAT ARM
ASSEMBLY, and it's rather delicate, so be careful not to bump or bend it
while you work on the rest of the carburetor.  We'll talk more about this
assembly, later.

Just to the right of the MAIN JET is small opening, with a brass fitting
inside the opening.  The brass fitting should have a hole though it, and a
screwdriver slot in the top of the fitting.  This fitting is the IDLER JET.
It controls the fuel flow during engine startup, and up to about one-fourth
throttle setting.  Use a screwdriver to unscrew the IDLER JET, and then
carefully lift it out.  (Tweezers are very handy.)

There's not much to the IDLER JET, but like all carb jets it's critically
important that the tiny fuel orifice not be blocked with dirt or sediment.
Hold the IDLER JET up to a strong light, and peer down the end.  You should
easily be able to see a small dot of light shining through.  If you see no
light, or only a partial dot, the orifice may be blocked.  If so, blow it
out with some compressed air (or just blow on one end, like a whistle).  If
there is blockage in the jet, you may be able to dislodge it with a tiny
sewing needle.  But probe gently with the needle!  You certainly don't want
to break off the end of the needle inside the jet.

One trick for examining the interior of the IDLER JET, is to look at it
with a strong magnifying glass, while shining a strong light through the
magnifying glass.  (Hold the light next to your eye.)  This both
illuminates and magnifies the view inside the jet.

The size of the IDLER JET is stamped on the side of the jet.  Be sure you
have the right size.

Now let's look at the MAIN JET.  Slide the SIEVE SLEEVE off the body of the
MAIN JET, then unscrew the MAIN JET from the top of the assembly.  When in
place, all you can see of the MAIN JET is the hex base.  Be careful not to
drop down and unscrew the MIXING TUBE, instead of the MAIN JET.  A very
handy tool for this job is the BING QUICK CHANGE WRENCH.  It's just a
little knurled knob, with a built-in socket wrench on either side.  On the
skinny side is the fitting for unscrewing the MAIN JET.  On the opposite,
larger side, is the fitting for unscrewing the MIXING TUBE.  A very useful
tool to have.  Just $8 from California Power Systems.  Part #6924.

Carefully examine the MAIN JET to ensure that it's not blocked.  The MAIN
JET controls the fuel flow to the engine from approximately 3/4 power to
full power.  The MAIN JET is what you change when the temperature, or the
altitude of your flying field, changes drastically.  Having several
different sized MAIN JETS, to cover your likely operating temperatures and
altitudes, is a good thing.  With a little luck, the MAIN JET is probably
the only thing you will ever need to adjust on your carburetor.  The size
of the MAIN JET is stamped on the end of the jet, so you can determine what
size it is, without removing it from the carb.

Fortunately, changing the MAIN JET is also the easiest thing to adjust on
your carburetor.  You simply remove the float bowl, exposing the MAIN JET,
and unscrew it.  Screw in the new MAIN JET, replace the float bowl, and
you're ready to fly.

Now turn your Bing Quick Change Wrench over, and use the fat side to
unscrew the MIXING TUBE.  Lift it out and examine it for any signs of dirt
or damage.

Pick up the carburetor and carefully turn it over.  The NEEDLE JET should
slide out of the hole in the center of the carb.  Examine it for any signs
of dirt or damage.  The size of the NEEDLE JET is stamped on the side of
the jet, so you can check and make sure it's the right size.

As you may recall, the NEEDLE JET and the JET NEEDLE work together to
regulate your fuel flow from 1/4 to 3/4 engine speed.  Pick up the JET
NEEDLE and slide it into the small end of the NEEDLE JET to see just how
these two parts work together to control the fuel flow.  As you can see, as
the tapered needle slides into the NEEDLE JET, the orifice is increasingly
blocked.  Likewise, withdrawing the tapered needle increases the size of
the orifice in the NEEDLE JET, and consequently increases the fuel flow.

At this point, the only thing left in the center hole of the carb is the
ATOMIZER.  This is a small brass tube that is a tight press fit in the
center hole of the carb.  The NEEDLE JET fits up inside the ATOMIZER.  If
you look down into the top of the carb, you can see the top of the ATOMIZER
sticking up into the VENTURI.  Note that the ATOMIZER has a high side,
facing the air filter, and a low side, facing the engine.  If you ever find
it necessary to remove the ATOMIZER, be sure to orient it in the right
direction when you re-install it!

The only thing left on the carb is the FLOAT ARM ASSEMBLY.  This is the
little pair of brass arms that fit on either side of the center of the
carb, and rock up and down on a horizontal hinge pin.  When this assembly
hangs down, fuel can flow from the fuel line, and into the carburetor bowl.
As the bowl fills, the twin floats in the float bowl start to rise.  As
they rise, the horizontal brass pins on the side of each float touch the
two float arms and push the float needle valve closed, cutting off the
inflow of fuel.  As the fuel in the bowl gets sucked up, the floats drop,
causing the float needle valve to open again, and permitting more fuel to
flow into the bowl.

Normally the FLOAT ARM ASSEMBLY is only taken apart if you have fuel
leakage problems in the carb, or are rebuilding the carb.  It's a rather
delicate assembly, so let's just leave it alone for now.  If you need to
take it apart, or troubleshoot it, there is a detailed write up in the Bing
Carb Manual.  There are a couple of things you can check on the float arm
assembly, just by eyeballing it, so read the section in the Bing Carb
Manual, and learn how.  It's pretty easy.

Now let's re-assemble the carb.  First, screw the IDLER JET back into the
opening on the right side of the carb.  Next, if you removed the ATOMIZER,
make sure it's back in the center tube, and properly aligned.

Now slide the NEEDLE JET back into the center tube (narrow end first), then
slide the MIXING TUBE in after it, and tighten the MIXING TUBE with the fat
side of your Bing Carb Wrench.

Screw the MAIN JET into the end of the MIXING TUBE, and tighten it with the
narrow side of your Bing Carb Wrench.  Slide the SIEVE SLEEVE down over the
MIXING TUBE.  Leave the end of the SIEVE SLEEVE aligned with the end of the
MAIN JET.  The SIEVE SLEEVE will properly re-seat itself when you put the
float bowl back on.

Before you put the float bowl on the carb, check to be sure that both carb
floats are mounted on their vertical pins inside the float bowl, and are
free to slide up and down the vertical pins.  Check the gasket that goes
between the float bowl and the body of the carb, then slide the float bowl
up into place on the carb.  There is a slender brass tube that slides into
a hole on one corner of the carb.  Once the float bowl has been
re-installed on the carb, slide the heavy metal clip over the base of the
bowl to lock it in place.  Make certain that the clip is pushed all the way
against the raised metal stops on either side of the bowl.  You don't want
the bowl to fall off in flight!

Now let's remount the carburetor on the engine.  Push the metal lip on the
side of the carb (opposite the air filter) into the rubber flange on the
side of the engine.  Make sure the metal lip goes all the way into the
rubber flange.  Put the metal clamp over the end of the rubber flange (just
follow the groove in the rubber), and tighten the clamp.  We don't want the
carb to fall off the engine, in flight!

Now screw the choke cable fitting back into the top of the carburetor on
the right side.  This will usually be easier to do if you first apply the
choke, since this pulls the spring-loaded piston back into the choke
fitting, and makes it easier to get the fitting into the threaded hole.
When the choke cable fitting has been screwed down tight, slide the rubber
boot back down over the top (if it's not already there).

Now let's re-assemble the throttle valve piston assembly.  First, reduce
the engine throttle to minimum setting, to give yourself as much cable
slack at the carb end of the cable, as possible.  Then check the JET NEEDLE
and make sure the E CLIP is on the proper needle slot position.

Make certain the tiny rubber o-ring is pressed over the top end of the JET
NEEDLE (the end opposite the sharp, tapered end), and slide the o-ring down
against the E CLIP.  Don't worry about having the o-ring actually press
against the E CLIP; that will be done automatically when the unit has been

Now slide the JET NEEDLE, tapered end first, down inside the piston, and
through the center hole.  Let the JET NEEDLE emerge from the bottom of the
piston.  The tapered end of the needle should hang a couple of inches below
the bottom of the piston.  The E CLIP on the needle should seat itself into
a cradle at the bottom of the piston, and should only fit into the piston
one way.

Now thread the white SPRING CUP onto the throttle cable.  The PIGTAIL on
the end of the throttle cable should slide through the hole in the center
of the white SPRING CUP.  The nubbin side of the white SPRING CUP should be
facing away from the lid of the carburetor.

Check the underside of the lid of the carburetor, and make sure the large
rubber o-ring (about two inches in diameter), is still on the underside of
the lid.  The o-ring generally sticks to the underside of the lid, but once
the residual gasoline has evaporated, it sometimes falls off.  More than
once, I've found it lying on the floor.

Now thread the PIGTAIL down into the piston, and slide it through the large
hole near the edge of the piston (not the center hole!).  Let the throttle
cable drop down through the connecting slot, and into the pigtail anchoring
hole next to the center hole in the piston.  The center hole should
currently be occupied by the JET NEEDLE.  Pull on the throttle cable to
slide the PIGTAIL into the pigtail anchoring hole.  Maintain slight tension
on the throttle cable to keep the PIGTAIL from slipping out of its
anchoring hole.  Now slide the white SPRING CUP into the piston.  The
nubbin end on the SPRING CUP slides in first, and the SPRING CUP itself
will slide inside the piston on three separate guides around the edge.  Let
the white SPRING CUP slide all the way to the bottom of the piston, where
it should rest on the rubber o-ring on the E CLIP.  With the white SPRING
CUP in place at the bottom of the piston, the white nubbin on the white
SPRING CUP should be extending just slightly below the bottom of the
piston.  With the white nubbin in place in the hole, the PIGTAIL is
securely locked into its own anchoring hole next to the JET NEEDLE, and
cannot slip out.

Finally, re-install the spring.  Open the bottom end of the spring, and
slide the throttle cable between the end of the spring, and the first coil
of the spring.  Start rotating the spring, and the spring will
automatically "screw" itself back onto the throttle cable.  Turning the
spring will become somewhat harder as the tension in the spring starts to
build up. You may have to finagle it a bit.  Once the spring is back on the
throttle cable, make certain one end of the spring is re-seated in the hole
in the underside of the carb lid, while the other end of the spring is
seated inside the white SPRING CUP at the bottom of the piston.

Now let's put the piston assembly back into the top of the carburetor.
Being careful not to bang the end of the JET NEEDLE, slowly lower the
piston assembly back into the barrel of the carburetor.  There is a guide
slot down one side of the piston, and a guide nubbin down the right hand
wall of the carburetor barrel.  Make sure the guide nubbin fits smoothly
into the guide slot in the side of the piston.  In other words, the piston
will only fit into the barrel ONE WAY, so be sure you have it oriented
properly, and DON'T FORCE IT.  The piston should slide all the way to the
bottom of the barrel.  If it doesn't, try turning the piston slightly, one
direction or the other, until it slides smoothly all the way to the bottom
of the barrel.  You should end up with the lid of the carb resting on the
top of the carb, with only a slight upward push from the big spring inside
the carb.

Screw the two carb lid screws back into the body of the carb, to secure the
lid.  The carb lid may look like it will fit, either way, but it won't.
There's a small pin on one side of the bottom of the lid that fits into a
hole on the body of the carb.

That's all!  You've successfully taken the carb apart, and reassembled it.
Now you know how to locate and change a Main Jet, Idler Jet, Needle Jet,
Jet Needle, and E Clip.  In addition, you can check your carb from time to
time, and make certain that all the parts are clean and working properly.
If problems start to develop in your carburetor, you can open it up and
take a look, instead of just trying to wish them away.  This knowledge will
make your flying much safer.

Happy flying!

Chris Wolf