Don't Be Left in the Dust; Clean Those Carbs!

Don’t Be Left in the Dust; Clean Those Carbs!

by: J. Montgomery Spencer

With the first time purchase of a motorcycle, most people opt to buy a smaller displacement bike of Japanese origin. The advantages of this is their relative simplicity and overall ease of use. However, to safely operate the motorcycle and achieve expected performance, maintenance and timely carburetor cleaning are key. While all bikes have very different carburetors, their functions are the same. Likewise the cleaning procedures are mostly universal throughout the industry.


Before starting, make sure you have a pair of OSHA approved safety glasses. Carburetor cleaning involves the use of compressed air, pressurized caustic chemicals, and small, sprung parts that want nothing more than to blind you for life. A rule of thumb is not to pick up a wrench without your eyes properly protected. Accidents happen every day, and are common among mechanics young and old.

The first job in carb cleaning is the removal of the carburetor or carburetors from the bike. This varies from one model bike to the next, and even within the same models of different vintage. In most cases a cheap manual will have the proper procedures for carburetor removal. The key to carb extraction lies in four actions: shutting off and emptying of fuel from the carbs, disconnecting the rubber manifolds from both sides of the carbs, disconnecting the throttle and choke(if applicable) cables, and extraction of the carb or carbs from the bike for further disassembly.

To prevent fuel from getting all over the place and creating a fire hazard, shut off the fuel line at the petcock. If this function is not available, then it is done automatically. Now you must drain the remaining fuel from the carburetor bowls. This is usually accomplished by loosening the drain screw at the bowels’ lowermost portion. Do not force this action. If the screw does not want to move, leave it for removal later in the cleaning when heat can be applied. Now the gas can drain from the gas line and carbs to a pan under the bike.

In many cases you’ll find that motorcycle carbs are held in place only by the rubber manifolds to the engine and from the air-box. They are almost always held in the manifolds by screw clamps. These can be removed with a screwdriver in nearly all cases. If the air-box is to be removed, now would be the best time to do so. Also it may be necessary to remove the gas tank at this point. This not only frees up working space, it prevents common mishaps involving sharp tools and painted metal. If further working space is needed, the manifolds can be removed entirely.

There are two different designs in throttle cables. One is a single pulling cable, the other is a duel push-pull cable. The single cable is easily removed by actuating the throttle by hand and sliding the now limp cable out of the throttle assembly. The duel cable set-up will require finding the cable adjustments and loosening the cables for maximum slack. The cables can now be removed one at a time using the previous method mentioned. If a choke cable is employed, it can also be removed as mentioned above.

The carb or carbs can now be removed from the bike’s frame. If the carbs are connected on a rack, they should be extracted in one piece. If they are free floating of each other, then most likely they are already in your hand and out of the bike. If the carbs do not come out with ease, you may use a pry-bar or large handle screwdriver to carefully pry the carbs out. Now that the carburetors are out, you may place them on a workbench for further disassembly.

The next step in carb cleaning is removal of the bowls, floats, jets, needles, and slide assembly. With the carbs on a clean towel, unscrew the float bowls and lay them out in the order of removal. If the bowls are held in with screws at the lip, remove those screws first. The carb parts are not interchangeable, so keep all parts in order pertinent to the carb they came from.

The floats are attached at one end by a hinge that is free floating. This can be removed by pressing a pick or very small screwdriver into one side of the hinge. The floats can now be removed, as well as the attached float needles. Inspect these parts for cracking in the floats or obvious amounts of fuel in them. Also pay careful attention to the tip of the needles for warp or rot in the rubber. If any abnormality is detected, those parts must be replaced before the carbs can be reassembled.

The large main jet and smaller idle jet can now be removed. In most cases a long thin screwdriver is used. Unscrew the jets and allow them to fall out of the carburetor body. If the carb is of a CV (constant vacuum) design, an air-bypass jet will be found at the rear opening of the carb. This can also be removed in the same method. Inspect the jets. If blockage of any kind can be detected, try and remove it with a piece of solid wire. To fully clean the jets, take a can of carburetor cleaner spray with the directional hose attached and spray liberally in and on the jets. Now using an airgun with at least 100 psi of pressure, spray the jets until all carb cleaner has been removed. If this does not leave the jets clean, repeat as necessary. Place the jets in their appropriate order with the floats and float bowls.

The carbs can now be turned upside down to remove the CV assembly (if equipped), the slides, and main needles. In the case of a CV type carb, remove the screws holding the vacuum plate to the top of the carb body. With that removed, the diaphragm and attached parts will slide out. In non CV applications, merely unscrew the top of the carb body and remove slide and attached needle. If there is any resistance in the slide assembly when removing, or if any dirt, gunk, or chalky buildup is seen, clean with carb cleaner and lightly brush with 0000 fine steel wool. Spray with the air gun to remove any particles that remain.

Now with the entire carburetor disassembled, you have a tough choice to make. Is it enough to have the internal components nice and shiny, or does the outside need to match? You can go about polishing the external parts of the carburetor using two different methods.

The first is very easy, inexpensive, and fast Start out by taking all of the cast aluminum and chrome parts from a single carburetor. Using a polishing paste, obtained at any automotive store, apply paste to external parts as directed by the polish manufacturer. This will give you a brilliant shine that will last a few months. Repeat for each carb, making sure to place the external parts with proper internal parts.

The other method is more involved, will take a good deal of time, and requires some specialized equipment. You’ll need a bench grinder, buffing wheels, and a number of different grade buffing compounds. A good hardware store should stock these items with specific instruction for obtaining a shine that will last all season and impress the hell out of your friends. After polishing the external parts, be sure to spray those parts down again with carburetor cleaner and the air hose to remove any buffing compound that may have snuck into the internal sides.

Now that your carbs are clean, the process of reassembly can begin. In most cases you will install the carburetor parts in reverse order that they were removed. The slide assembly can be installed last if a non CV system is employed. This will clear up some space for installing the carbs on the bike. Be sure to check the height of the float needles before attaching the carb bowls. A cheap manual should explain this procedure and carb synchronizing, which will be necessary for obtaining peak performance.

With all parts installed and attached, you can now start the bike. It may take a while for the gas to fill all fuel passages and get the bike running smoothly. At the same time, keep your hand on the motorcycle’s kill switch. A freshly cleaned carb may send the motorcycle’s engine past its red-line when first started. This is a sign that a few tuning procedures must follow. Fear not, you’re just another hour from being leader of the pack.

"Look out! Look out! Look out! Look out!"