Disassembling The Bing Carburetor

Recently I've been engaged in attempting to learn as much as possible aboutmy Bing 54 carburetor. I've read all the articles in the CPS catalog, andordered and read the Tuning & Parts Manual from the Bing agency in Kansas.(1-800-309-2464)

Both the articles, and the manual, have a great deal of useful informationon how the carb works, and how to tune it. But nowhere in any of thisinformation is there a detailed write-up on how to take the carb apart andthen re-assemble it. There are exploded parts diagrams, to be sure, butthat's not the same thing as having a detailed write-up. And there aresome aspects of carb disassembly that can be positively baffling if you'venever done it before.

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

However there's no reason for this, since it's actually quite easy to openthe carb up, and check your jets (and all the rest of the parts). Andsince the Bing people also recommend that the carb be rebuilt every 100hours, it seems to me that every PPC pilot should know how to open up hiscarb, 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 auseful thing to pass on to the rest of the PPC pilots. Certainly in allthe years I've been compiling information on PPC engines, I've never seenthis done anywhere.

So here is my documentation on how to take the Bing 54 carb apart, and putit back together, and how to check and adjust the jets. It's written fromthe point of view of a complete novice (which is what I was, until veryrecently). I won't guarantee that my write-up is 100% accurate, but it isas accurate as I can make it at my current level of knowledge. If thereare any errors, please let me know so that I can correct them. Dependingon how old your carbs are, how many you have, and what sort of air filteryou have, your setup may not exactly match mine, but it should be prettyclose. 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 anovice to delve into the guts of the carb, if he's not squatting next tothe 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 thelittle metal nipple in the side of the carb, I just cut the line off andreplace it later. Fuel line is very cheap, and easy to replace. Whystruggle just to save a few pennies?

There are two cables running into the top of the carburetor; the throttlecontrol, and the choke control. The choke control is on the right, whilethe throttle control is in center of the top of the carb. The chokecontrol is a brass fitting, about an inch long, with a hex nut base and askinny 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 themetal body of the carb. Once the fitting is unscrewed, lift the entirechoke control assembly out of the body of the carb. You should see alittle piston, about half an inch long, on the end of the fitting, with apowerful spring behind it, trying to push it out of the body of the brassfitting. 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 wemust 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 designedto stay with the lid.

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

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

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

By the way, if you're having trouble keeping the difference between the JETNEEDLE 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. Inother words, the NEEDLE JET is the jet at the bottom of the carb, and theJET NEEDLE is the long, tapering needle that is lowered into the NEEDLEJET. Go back and read this section a couple of times, if necessary, until

the difference between the NEEDLE JET and the JET NEEDLE is perfectlyclear. It's really pretty simple, but it's easy to get the two mixed upwhen you're just getting started.

What else do we see when we look down into the carburetor? Well, there's abig 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 theengine. This passageway is called the VENTURI. It's where the fuelactually gets injected into the incoming airstream.

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

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

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

The JET NEEDLE, hanging down from the body of the piston, comes in severalsizes and tapers. If your engine is not running smoothly, it can sometimeshelp to change to a different size needle. However, before you can changethe needle, you need to be able to get it out of the piston. To take thepiston 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 thespring off of the throttle cable when it's being held at both ends by thecarb 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 thelid, and force the throttle cable between the very end of the spring, andthe next coil of the spring. Then start rotating the spring. It willquickly "unscrew" itself from the throttle cable. Voila! Now with thatdamned spring out of the way, you can easily disassemble the remainder ofthe piston assembly.

Look at the bottom of the piston. Right next to the JET NEEDLE, you willsee a little white nubbin sticking out of a hole. This nubbin is part ofthe 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, ortoothpick, and push the nubbin back into the piston until the hole isclear.

With the nubbin out of the way, you can free the throttle cable PIGTAILfrom the bottom of the piston. The PIGTAIL is a little metal plug,soldered to the end of the throttle cable. The PIGTAIL anchors thethrottle cable to the bottom of the piston, so that when you pull on thethrottle cable, the PIGTAIL causes the piston to be lifted up, which pullsthe JET NEEDLE out of the NEEDLE JET, which allows more gasoline to flowinto 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 thatwas formerly occupied by the nubbin on the SPRING CUP. In fact, the twoholes are connected by a slot. Grab the lid of the carburetor and pull ittoward the piston. This will give some slack to the throttle cable, andshould cause the PIGTAIL to slide out of its anchoring slot and flop aroundfreely. Push the throttle cable up through the connecting slot, and intothe hole formerly occupied by the white nubbin on the SPRING CUP. (Ithelps if the hole is on the bottom, so that gravity assists you in gettingthe cable into the hole, rather than fights you.

Once the throttle cable is in the hole, pull the piston and the carb lidapart. The PIGTAIL should slide out through the hole, and will be free ofthe piston. The white SPRING CUP should also slide out of the piston. Ifnot, grab the spring cup with a pair of needle nose pliers, and slide itout of the piston.

At this point, the throttle cable, with the PIGTAIL on the end, and thewhite SPRING CUP should be removed from the piston. The only thing stillleft in the bottom of the piston is the JET NEEDLE. Slide it out of thepiston. Be careful. The JET NEEDLE assembly is kind of delicate. Don'tbend it!

Set the piston aside, and let's take a closer look at the JET NEEDLEassembly. At the top of the JET NEEDLE is a little metal clip (called theE 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 howold 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. Ifyou're having trouble getting your engine to run at a constant speed in the4500 to 5500 rpm range, it may be too rich, and moving the E CLIP up, oneor two notches, may cure the problem. But if you move the E CLIP, keep aneye on your EGT readings to make sure you haven't leaned the engine toomuch!

If you look closely at the E CLIP, you'll see that it has a break in themetal, right next to the curved part of the clip that snaps around the bodyof the JET NEEDLE. This is as it should be. Rest assured that you didn'tbreak the clip when you pulled the JET NEEDLE out of the piston. (Ofcourse 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 indiameter. This o-ring should slide down over the top of the JET NEEDLE andsnug up against the E CLIP. The purpose of this o-ring is to keep the JETNEEDLE from spinning inside the E CLIP, and getting sawed in two. If youdon'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. Nowlet's remove the float bowl from the carb and explore the inner workings ofthis amazing little gadget. The first thing we need to do is remove thecarburetor from the engine. Note that the carburetor is attached to theengine 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 theouter clamp holding the carburetor (no need to remove the inner clamp).When the outer clamp has been loosened, you can pull the carburetor out ofthe rubber flange.

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

Inside the float bowl, you will see two small floats (and probably somegasoline). 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'stake a look at the guts of the carb.

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

Just to the right of the MAIN JET is small opening, with a brass fittinginside the opening. The brass fitting should have a hole though it, and ascrewdriver 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-fourththrottle setting. Use a screwdriver to unscrew the IDLER JET, and thencarefully lift it out. (Tweezers are very handy.)

There's not much to the IDLER JET, but like all carb jets it's criticallyimportant 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 shouldeasily be able to see a small dot of light shining through. If you see nolight, or only a partial dot, the orifice may be blocked. If so, blow itout with some compressed air (or just blow on one end, like a whistle). Ifthere is blockage in the jet, you may be able to dislodge it with a tinysewing needle. But probe gently with the needle! You certainly don't wantto break off the end of the needle inside the jet.

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

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

Now let's look at the MAIN JET. Slide the SIEVE SLEEVE off the body of theMAIN JET, then unscrew the MAIN JET from the top of the assembly. When inplace, all you can see of the MAIN JET is the hex base. Be careful not todrop 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 alittle knurled knob, with a built-in socket wrench on either side. On theskinny side is the fitting for unscrewing the MAIN JET. On the opposite,larger side, is the fitting for unscrewing the MIXING TUBE. A very usefultool to have. Just $8 from California Power Systems. Part #6924.

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

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

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

Pick up the carburetor and carefully turn it over. The NEEDLE JET shouldslide out of the hole in the center of the carb. Examine it for any signsof dirt or damage. The size of the NEEDLE JET is stamped on the side ofthe 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 toregulate your fuel flow from 1/4 to 3/4 engine speed. Pick up the JETNEEDLE and slide it into the small end of the NEEDLE JET to see just howthese two parts work together to control the fuel flow. As you can see, asthe tapered needle slides into the NEEDLE JET, the orifice is increasinglyblocked. Likewise, withdrawing the tapered needle increases the size ofthe 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 theATOMIZER. This is a small brass tube that is a tight press fit in thecenter hole of the carb. The NEEDLE JET fits up inside the ATOMIZER. Ifyou look down into the top of the carb, you can see the top of the ATOMIZERsticking 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 findit necessary to remove the ATOMIZER, be sure to orient it in the rightdirection when you re-install it!

The only thing left on the carb is the FLOAT ARM ASSEMBLY. This is thelittle pair of brass arms that fit on either side of the center of thecarb, and rock up and down on a horizontal hinge pin. When this assemblyhangs 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. Asthey rise, the horizontal brass pins on the side of each float touch thetwo float arms and push the float needle valve closed, cutting off theinflow 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 toflow into the bowl.

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

Now let's re-assemble the carb. First, screw the IDLER JET back into theopening 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), thenslide the MIXING TUBE in after it, and tighten the MIXING TUBE with the fatside of your Bing Carb Wrench.

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

Before you put the float bowl on the carb, check to be sure that both carbfloats are mounted on their vertical pins inside the float bowl, and arefree to slide up and down the vertical pins. Check the gasket that goesbetween the float bowl and the body of the carb, then slide the float bowlup into place on the carb. There is a slender brass tube that slides intoa hole on one corner of the carb. Once the float bowl has beenre-installed on the carb, slide the heavy metal clip over the base of thebowl to lock it in place. Make certain that the clip is pushed all the wayagainst the raised metal stops on either side of the bowl. You don't wantthe bowl to fall off in flight!

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

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

Now let's re-assemble the throttle valve piston assembly. First, reducethe engine throttle to minimum setting, to give yourself as much cableslack at the carb end of the cable, as possible. Then check the JET NEEDLEand 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 JETNEEDLE (the end opposite the sharp, tapered end), and slide the o-ring downagainst the E CLIP. Don't worry about having the o-ring actually pressagainst the E CLIP; that will be done automatically when the unit has beenreassembled.

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

Now thread the white SPRING CUP onto the throttle cable. The PIGTAIL onthe end of the throttle cable should slide through the hole in the centerof the white SPRING CUP. The nubbin side of the white SPRING CUP should befacing away from the lid of the carburetor.

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

Now thread the PIGTAIL down into the piston, and slide it through the largehole near the edge of the piston (not the center hole!). Let the throttlecable drop down through the connecting slot, and into the pigtail anchoringhole next to the center hole in the piston. The center hole shouldcurrently be occupied by the JET NEEDLE. Pull on the throttle cable toslide the PIGTAIL into the pigtail anchoring hole. Maintain slight tensionon the throttle cable to keep the PIGTAIL from slipping out of itsanchoring hole. Now slide the white SPRING CUP into the piston. Thenubbin end on the SPRING CUP slides in first, and the SPRING CUP itselfwill slide inside the piston on three separate guides around the edge. Letthe white SPRING CUP slide all the way to the bottom of the piston, whereit should rest on the rubber o-ring on the E CLIP. With the white SPRINGCUP in place at the bottom of the piston, the white nubbin on the whiteSPRING CUP should be extending just slightly below the bottom of thepiston. With the white nubbin in place in the hole, the PIGTAIL issecurely locked into its own anchoring hole next to the JET NEEDLE, andcannot slip out.

Finally, re-install the spring. Open the bottom end of the spring, andslide the throttle cable between the end of the spring, and the first coilof the spring. Start rotating the spring, and the spring willautomatically "screw" itself back onto the throttle cable. Turning thespring will become somewhat harder as the tension in the spring starts tobuild up. You may have to finagle it a bit. Once the spring is back on thethrottle cable, make certain one end of the spring is re-seated in the holein the underside of the carb lid, while the other end of the spring isseated 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 thepiston 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 handwall of the carburetor barrel. Make sure the guide nubbin fits smoothlyinto the guide slot in the side of the piston. In other words, the pistonwill only fit into the barrel ONE WAY, so be sure you have it orientedproperly, and DON'T FORCE IT. The piston should slide all the way to thebottom of the barrel. If it doesn't, try turning the piston slightly, onedirection or the other, until it slides smoothly all the way to the bottomof the barrel. You should end up with the lid of the carb resting on thetop of the carb, with only a slight upward push from the big spring insidethe carb.

Screw the two carb lid screws back into the body of the carb, to secure thelid. 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 ahole 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 totime, 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 andtake a look, instead of just trying to wish them away. This knowledge willmake your flying much safer.

Happy flying!

Chris Wolfcwolf41@home.com