Bing carburetor tuning, Bing carburetor troubleshooting, and Bing carburetor disassembly procedure.

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Bing Carb Tuning and Troubleshooting

When a person is ill an instrument that is frequently used is a thermometer. When an ultralight engine is "ill" its thermometer is the spark plug. A properly tuned engine will come out with a nice sandy brown or tan coloured spark plug. An spark plug that comes out grey to white indicates a lean fuel mixture  while a plug that comes out black, wet or sooty looking indicates a rich fuel mixture.

Now if you are looking for a problem the spark plug can also help trace the problem. A spark plug that is dry after several attempts to start it would indicate that no fuel is getting to the engine. While a spark plug that is wet would indicate a rich or flooding situation.

Since the fuel that causes these two situations is supplied by the carburetor lets take a closer look at this unit. Experience has shown that usually one of two thing happen if the carburetor is involved in the problem. First either something has worn over a period of time and has gradually effected the performance of the engine, or something happens instantly. Of course something can  wear over a period of time and  fail causing the instant situation.

Now before we get further into this - the following is for troubleshooting and tuning a BING carb. Before you start into it you want to make sure that your problem is with the carburetor. If the engine that you are working on has seized rings, or a blown piston, wrist pin bearing, or faulty spark plug, cap or ignition coil - you will be wasting your time trying to "tune or troubleshoot the carb."

In order to do the following properly you should have an EGT gauge correctly installed with probes for each cylinder and a tachometer.

One of the easiest ways to check for damage to a two stroke engine is to remove the exhaust manifold. With this done you can see the pistons, rings etc. If there is any damage, blow bye, or ring seizure forget about your carb and fix the real problem.

Your engine won't start and the plugs are wet.
This indicates excessive fuel in the combustion chamber. This can come about IF YOU HAVE NO SPARK -which is not carb related. It can also occur if the float level is too high, or if a component such as your float(s), float arm, needle, seat are damaged or obstructed.
It can also occur if your "enriching circuit" has been used to much, or you have primed the engine too much. Engines that are used inverted will generally be found in this condition after a day or two of storage, this is not a carb problem! To start this engine DO NOT prime it - give it full throttle and crank it until it either starts or clears itself.
Suggestions: The first thing that I do when checking for proper fuel level in the carb bowls is to check the  floats.In looking at the float I am looking for damage, this usually occurs around the pin hole that goes through the center of the float. To check the floats  fill the float bowls with fuel lay them on a flat surface and then place the floats on the stems. Note where the float arms are in relation to the fuel. Let them sit there for about 15 minute and then check them If fltlevel.gif (4705 bytes)the floats are not level with each other then and both arms are not even with the top of the fuel them the float(s) are damaged and need to be replaced. A float like this will cause an improper fuel mixture since it allows more fuel in than it should. Also because only one float is working the other is taking more of the load and it will sink.
Next turn the carb body upside down on a float surface. The two float arms should be LEVEL with the base of the carb. You adjust this by bending the CENTER tang where the needle rides. DO NOT bend the float arms.
If fuel is running out the over flow tube then your needle and seat has either failed or an obstruction is preventing it from closing.  To repair this you will have to remove the float arms and needle and then use compressed air to clean the passage way. It is suggested that you use a plastic bag over the other end of the passage when you use the air. This way you can verify what was obstructing the needle and that it has been removed.

Your engine won't start and the spark plugs are dry.
Dry spark plugs usually can be traced to fuel not getting to the carb, a plugged low speed jet, or the use of throttle when using the choke system. So find out why fuel isn't reaching the carb - e.g. - turn the fuel on - clean the low speed jet - when using the choke system the throttles MUST BE AT THE IDLE POSITION - the choke does not work if the throttles are even cracked a small amount.

In order to do the following properly you should have an EGT gauge correctly installed with probes for each cylinder and a tachometer.

Engine starts but won't idle.
You don't have the slides in the carbs set correctly - refer to Tech tips 1 for the proper way to set up the slides. The low speed jet is plugged - clean it. Your low speed airscrew is adjusted incorrectly - refer to the bing carb jet chart for proper airscrew setting .

This air screw changes the air/fuel mixture by changing the ratio of air to the idle jet circuit. Turning the screw out with lean the mixture while turning it in richens it.
After referring to the jet chart you have a position to start from.  With the engine warmed up and idling and the screw set to factory specs turn the screw out very slowly - the engine should start to pick up rpm as you lean the mixture out. If nothing happens the low speed jet is probably plugged, or the small atomizer hole located in the throat of the carb  on the engine side is blocked.
Once you have the engine idling at its highest and leanest setting using the air screw turn the screw back in 1/8 of a turn which will richen it up just enough for the best performance.
Note it is usually necessary to do this three or four  times a year, do to the difference in air that you get in spring/summer/fall/winter. Note that on the 582 Rotax I have found that 45 and 50 idle jet work better than the standard 55 especially in winter. On the 582 the lower jet sizes have been shown to improve starting and help eliminate the rough idle.
A quick way of checking your mixture is to let the engine idle for a few minutes and then apply a burst of throttle. If the engine bogs it usually means your mixture is too lean. You can verify this by applying throttle then choke - which richens the mixture of course if the bog goes away then you have too lean of a mixture.
You can also change the mixture using the needle and clip - but remember this changes everything from idle to 3/4 throttle. Raising the clip - thus lowering the needle leans the mixture - while lowering the clip and raising the needle richens it.

Engine RPM varies at and idle - won't remain steady.
This is usually caused by an air leak. A failed intake manifold gasket. A crack in the intake manifold. If you have had the intake manifold off, the gaskets can fall down inside the cover. If you have had the cylinders off and don't use the proper alignment bar during reinstallation you can crack the intake manifold. A failed rubber O ring in the top of the carb cover plate. The rubber stopper covering the primer inlet has failed or is missing. Water in the bottom of the float bowl.

Engine sputter or misfires (0 - 1/8 throttle)
This area is controlled by the low speed or idle jet, and air mixture screw. Check to make sure the jet is clean and the proper size. Check to see the air mixture screw is set correctly.

Engine sputter or misfires (1/8 - 1/2 throttle)
This generally indicates a lean fuel mixture. Check to make sure your needle and clip are in the right position and are not damaged. The air screw still has some effect here.

Engine sputter or misfires (1/2 - 3/4 throttle)
This area is controlled by the needle jet and jet needle. Verify that you have the correct jet and needle jet. Also verify that they are located BELOW the white plastic retaining cup. If they are located on top of the retainer the engine will run rough in all ranges, since the mixture is wrong in all locations.
The mid range is controlled by the needle and needle jet. The needle jets are available in various sizes with the larger numbers giving a richer fuel mixture and the lower numbers a leaner mixture.

A reported problem with ALL bing carbs is with failure of the jet and or needle clip. This can result in erratic running, lean fuel mixtures, engine returning to and idle during flight.
Click here for the latest Update Information - with solution to problem!

To determine whether you need to adjust the needle jets you require a EGT gauge and tachometer.
For example:
Many owners of 582's have reported high EGT readings in the 5600 to 5800 rpm range using the stock needle jet of 272 - using a 274 or 276 eliminates this problem.
Owners of older model 532 report having a problem keeping the engine set at 5400 rpm. It would jump up and down from 5400 to 5800 resulting from  a lean fuel mixture. Again the larger jet usually cures this problem.

Engine sputter or misfires (3/4 to full throttle)
This area is controlled by the main jet. Check to make sure it is in place and snug. Make sure there is no water in the bottom of the float bowl. Make sure the needle and clip are in good working condition. If the needle fails around the clip retaining area this will allow the needle to jump up and down causing erratic running. Proper float level is also important here to little fuel flow can cause an lean mixture while to must flow can result in a rich mixture.
One area that is of concern is in higher altitudes and colder climates. Higher altitudes usually require leaner fuel settings - lower size main jets, while colder temperatures require increased jet sizes to compensate for the thicker air. 
Consult the Bing jet chart for proper jet recommendations.

Now if you are tuning your carb using the above these have to be present!
1. The engine has to be in good working order.
2. The engine has to have the proper prop load.
3. The engine, exhaust etc all have to be STOCK, as supplied or recommended from the factory or knowledgeable/authorized person.

Also check out Setting up your Rotax engine

Disassembly - Carburetor

Tools Required
Flat blade screw driver (supplied in Rotax tool kit)\..
Phillips screw driver
Small adjustable wrench

Shop supplies
PJ 1cleaner


To disconnect carburetor from engine loosen clamps holding carburetor to rubber flange intake boot.Gently pull and the carburetor will separate from the boot. To remove the top loosen the two retaining screws the top of the carb will come off . To remove throttle cable, compress the carburetor piston spring (1), push the white plastic spring cup   out of the carburetor piston (7), move the throttle cable side ways in the carburetor piston, this allows it to release through the larger hole in the bottom of the piston. Remove the jet needle (2) and retaining clip (3). Be careful not to loose the rubber sealing ring  located in the carburetor cover plate.

With the top removed place the carburetor on the bench upside down. Slide the bowl spring clip side ways and the carb bowl will come free. (It may be necessary to gently tap the bowl, to break it free from the bowl gasket). Carefully remove the gasket.

Disassembly - Carburetor

In the center of the carburetor covering the main jet   (6) will be a sieve sleeve,  (this looks like a little filter) remove it (its purpose is to stop foam from entering the main jet).

Looking at the top of the main jet you will see a number, this indicates the size of the jet. For jets specifications refer to 
Bing jet chart for proper jet recommendations.
. Remove the main jet (6) . Remove the mixing tube,  this will allow removal of the needle jet (5).

Located beside the main jet is an orifice containing the idler jet (4). Using a small screw driver (supplied in Rotax tool kit), remove the idler jet.

Next remove the float pin, (7) this will allow removal of the float bracket,  or float depending on which type your engine is using.

Under the float bracket is the float needle and float needle clip remove them. Two screws, one large one small, are located on the side of the carburetor. The larger screw with the spring under it is the idle (11) adjustment screw . The smaller with the rubber ring under it is the air regulating screw (10).


The correct order of the jet needle,retaining clip, plastic spring cup, and spring, in the carburetor piston.

Note: On some models the floats are part of the float bracket, while on others the floats are separate, and move on two locating pins in the float bowl.

Reassembly - Carburetor


Using a general purpose cleaning solvent clean all the parts. Check the main jet and idler jet orifices to ensure that they are not plugged.Using compressed air blow through the vent holes, main jet, and idler jet.


Place the carb body on the bench inverted. Replace the needle jet, mixing tube, and thread the main jet into the mixing tube.

Install the needle jet and needle clip, install the float bracket, or float. If proper adjusted the float bracket arms should be level when the carburetor is sitting inverted on the bench. Now turn the carburetor right side up and check to make sure that the needle valve is not sticking.Invert the carb once more.Install the idler jet.

Install the float chamber gasket, seeve sleeve. Install the floats (depending on carb style). Install bowl gasket. Install float bowl and lock into place with the spring clip. Turning carburetor over install the spring and idle adjustment screw, Install the O ring and air regulating screw.

For engine idle speed and air screw adjustment refer to 
Bing Jet Chart

Install the throttle cable through the rubber grommet, then and top throttle cover plate. Make sure that the rubber O ring is in place under the cover plate. Install the carburetor piston spring. Install the white plastic spring cup over the end of the carburetor piston spring, using the cup compress the spring making sure the throttle cable protrudes through the correct hole in the spring cup. Install you jet needle, and holding plate into the carburetor piston. Place the throttle cable end into the piston and down through the hole in the side. Once through slide the throttle cable over, and up to lock it into position. Now allow the plastic spring cup to slide down over top of the spring clip. Install the unit into the throttle body making sure that the piston guide hole and carb body guide line up. Tighten up the two cover plate retaining screws.Slip the carburetor body into the rubber socket and tighten the retaining clamp.

It is recommended that all old float system carburetors be updated to current float system. Older system does not regulate as accurately as new one , and older system leaks excessively through float bowl over flow.

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