CX500/GL500                                                                                                     2012


Correct cleaning ,re-fitting and servicing of the Carburetors is paramount to full power and good Mpg.

The carburetors can vary from model to model but the basic internals are the same for servicing.Some models have the tank fuel pipe to the centre of the transfer pipe.Some models have an Accelerator Pump.Some fuel tanks have a Vacuum Petcock. You can use Cold White Vinegar to soak the carb bodies but NEVER on the Accelerator pump cover of those types of carbs!

Try not to split the carbs as they are a PITA to get back together.Also do NOT remove the Boots from the Air-box.It's not needed and they also are a right royal PITA to get back in the Air-box(Use Hairdryer to warm them up if have taken them out.It will make them easier to get back in).

Before doing any work on the carbs always check for Carb Boot leaks.
From the right hand side of the bike with the engine idling spray some Carb/Brake cleaner or Hairspray or WD40 type stuff around the carb boots on the Air intake and engine side of the boots and also shoot through to the left hand side inner boot areas.If the engine speed changes even the slightest in either direction there is a leak.

Repeat from the Left hand side of the bike.This is to make sure you get all round all possible areas where there can be an air-leak.These leaks can be really sneaky .


The tricks to these carbs

Important!(Low Speed Idle Circuit)
Bad idling/Low speed lack of power( 1,100 to 3,000 Rpm)
In the top of the Carbs there is a small Plastic/Nylon,"Black Banana<see diagram>".Under this are two Brass holes.Along with the other two brass holes on the tops of the carbs these are the most common blocked cause of low speed carburation problems.Clean out with loads of WD40/Compressed air/High pressure water and also you can use a Guitar String.These fine tubes(Venturi)  culminate as 3 fine holes around the Butterflies.These can be poked clean with a ,"Top E/B/G" string from a guitar.
    Polish the Slides with some Metal polish and check the Needle is not bent and clean off with Carb/Brake cleaner.The Black Plastic Seal ring goes on with the groove towards you.

Jets/Emulsion Tubes
Bad running/Lack of power(3,000 Rpm+)
In the Stock carbs there are two jets.The 78 which goes straight into the carb body and the 112(or 115) that goes into the Brass holder.There is a 3rd hidden one under the small Black,"Rubber Bung<see diagram>.You can remove the two main ones easy and boil them up in a pan with some washing soda crystals/washing up liquid.NEVER be tempted to poke these through with  anything metal as they are soft brass.You CAN use a hard nylon bristle from a brush.Then if possible blow them through with compressed air or Carb/Brake cleaner.
   For deep cleaning you can remove the emulsion tubes under the jets but I don't bother unless the carbs are really bad.There is information for this elsewhere on the net.A cold vinegar soak and blowing through with WD40 type stuff and Carb cleaner usually does fine.

Floats and Float Needle Valves(FNV)
Carb Overflow Leaks/Bad idle/Bad fuel delivery/General bad performance


The float heights MUST be set at 15.5mm from the Carb body(See manual).This setting is critical to correct fuel delivery.If ignored will Bite-You-In-The-A**.
      Plastic floats are not normally adjustable but if you heat them up with a Hairdryer you can sometimes get them to work by bending but you have to be careful not to break them.You cannot use a set of  Plastic Floats and their FNVs in a set of carbs that uses the Black Plastic/Metal floats as the FNV hole is a different length.A good machinist/engineer may be able to swap over the Brass tubes in an absolute emergency.

There is a Brass overflow tube inside the carb bowls.This has been known to split and cause carb overflow leaks.It can be repaired with solder and some people have even managed to replace it with another bit of fine tube.

Note:There is a small very tiny spring loaded plunger in on top of the Float Needle Valves.This must operate correctly.Press it down with your finger and make sure it moves up and down easily.You can free it up if seized with a bit of WD40 unless it's totally kaput.They come in the correct  carb/float kits for your model.

Air Cut-Off Valves(ACVs)
The Air-cut-off Valve assembly enriches the mixture when you close the throttle to avoid,"Popping"

There are two versions of these.One set has a slightly raised/domed cover and the others are flat.The Diaphragm parts have different length brass plungers so cannot be swapped,only as a unit.Get the right kits for your model of carbs.In the picture above it's the raised/domed type.Hold the diaphragm up to the light and if it has any holes or is damaged then look to replace the kit.There is also a very tiny O-ring(See diagram).If the ACVs are faulty you can,as a temporary fix,block the small hole where the O-ring goes with a dot of rubber.You may have to enrich the fuel mixture a little to help but some people have done this and never bothered replacing the ACV kit.

Carb Boot Leaks
After all the work that has been done cleaning the carbs one of the most common faults is actually introducing problems by not re-fitting the carb boots correctly and testing them for air leaks.

There are 6 points(3 on each side of the carbs<see Diagram>) where air can get into the system and cause no end of problems.The Hose clips are thin 8mm type.These are not always easy to source so I had to resort to some Cut-to-make ones as they can become stretched/weak.
If there are splits in the Carb boots you can  usually repair them with,"Shoe goo".Use Ebay for source.There is also a large O-ring that sits in a groove between the Carb boot and the engine.This must be in good condition and not left out.If you cannot find one I have seen this joint repaired with a gasket made of cardboard and RTV/Gasket sealant.

Back to Basics




web counter
web counter
000webhost logo