® The Spring Thaw: On-The-Bike CBX Carburetor Clean
Mike Nixon

Honda's CBX is of course the kind of machine that nowadays comes in for more than its share of restorative issues. Cleaning the carburetors is something nearly every owner has to grapple at some point. Here is a method that does the job while the carbs are still on the bike. It works well, if done carefully and according to these directions. However, the goal of this method is simply to fix a slightly gummed up carburetor. The machine shown here sat for eighteen months, and responded very well. But don't expect this method to work on a carburetor that has been sitting for eight years. If that's what you're up against, then just scroll down to the bottom of the page and check out the booklet offer. :-)


Here are a few of the tools you'll need. A hand-held mirror, some longish needle-nose pliers, a nice long #2 Phillips screwdriver, the factory carburetor idle mixture screwdriver (or its equivelant) and an aerosol can of Berryman's Chemtool B12 carburetor cleaner. There are alternatives to Berryman's too, such as Gumout and others. Just make sure what you pick contains either toluene or xylene. Aside from this, some assorted general hand tools (14mm wrench for example) may also be needed, as well as a face mask or respirator and some latex gloves.

Remove the upper rear engine hangers (the little triangular ones between the carbs) to get better access to allow room for some of the tops to come off. You don't need to remove the front engine hangers or lower the engine or any of that stuff.


It looks as if the number two (from the left) carb top will not come off, but actually it will, but just barely. Make sure you hold your tongue just right. :-P In extreme cases, you can loosen the rubber manifolds and push down on the carbs to get more clearance. If you do that, don't forget to retighten the manifold clamps later!

Once you get the tops off and slides out, check the slides for wear, damage, cocked needles (the needles should wiggle freely, they should not be bound up), amd most importantly, varnish. If they have much more than this (note the jet needle), the carbs may have to come off the bike to be cleaned correctly. This isn't too bad though. Click on the image to view a larger sample.


Remove the idle mixture ("pilot") screws, making sure you also retrieve the springs, washers and especially the tiny o-rings. The o-rings tend to jam into the casting and don't want to come out. If your idle mixture screws still have their emissions flags on them (they shouldn't) go to this link to see how to remove the flags so the screws may be removed. http://www.motorcycleproject.com/text/tech_videos.html#7

This cavity, the idle mixture screw cavity, must be bare. Take extra care to fish out the o-ring that tends to stick inside the casting. A bit of stiff wire works well to dig it out. If the o-ring was aftermarket and thus an incorrect size, it will probably be mashed pretty badly and need replacing. The good stuff from Randall Washington doesn't do that. You can get replacement o-rings from a Kawasaki dealer, part number 92055-1002.



Hold the hand-held mirror like this and with a flashlight, peek up into the mixture screw cavity. It you can't see shiny metal at the end of the hole, the o-ring is still in there. Get it out. The carburetor will not work right with the o-ring stuck in there sideways or torn. Click on this image to view a larger sample.

Take the spray hose from the Berryman's and sand or grind a taper on one end. This is important. This method relies on the force of the aerosol to be really effective. So don't skip this step. Click on this image to view a larger one.



Here we see the hose jammed (wedged) into the idle air bleed jet. Get it in there tight, and spray a few shots. Watch out for your eyes! Unscrew and remove the float bowl drain screw to let the cleaner out.

Repeat at all the idle air bleed jets, remembering that on the number 1 carburetor, the air bleed opening is hidden under the air cut valve cover and diaphragm. Don't lose the tiny o-ring inside the aircut valve cover when you remove it.



You should see cleaner come out of the idle mixture screw cavity each time the idle air bleed is blasted in each carburetor. Once you verify this, go back and blast the idle air bleeds in each carburetor again, only this time cover the idle mixture screw cavity with your finger and watch for discharge of cleaner from the idle port and transfer port inside the carburetor bore. This is a double-test and a way to back flush any varnish that's still in there. Click on this image to enlarge it.

Once the idle circuit is happy, move on to the other circuits, blasting and watching for discharge inside the carburetor where that circuit sprays out normally (at the outlet orifices). Shown is the secondary (or just) main air bleed jet being shot. Cleaner should bubble out inside at the center (bore) of the casting.



Here the primary main (1979 only) is being shot. Watch for cleaner discharging at the primary main outlet inside the carburtor bore.

Before reinstalling the idle mixture screws, you will want to modify them if you haven't already. The correct, factory way to eliminate the stops of the idle mixture screws is with a soldering gun or mini-torch. Heat up the aluminum flag and simply pull it off. You don't have to heat them much, but the parts will be hot, so be careful! If doing this on the bike, the flag must be heated with a 200+ watt soldering gun until too hot to touch, then carefully pulled (not pried) off.



Don't forget to clean out the glue from the mixture screw so that a screwdriver will fit into it properly. Click on the image to view a larger sample.

Now the idle mixture screw can be adjusted just like in the old days. Shown is the factory mixture screw adjustment screwdriver. An aftermarket type will work well also.



Before reinstalling the carb tops, gently clean their brass bores using a bit of brake cleaner or contact cleaner and a bottle brush. Don't use carb cleaner as it will strip the lacquer off the polished tops, and don't apply any lubricant.

It is not unusual to find grayish-green deposits on the slide's chromed shafts. This comes from the crankcase breather system, which feeds crankcase fumes into the air intake. Periodically clean this off and you will be rewarded with excellent working carburetors. To minimize this deposit, regularly purge the drain hose at the bottom of the air box. To avoid it altogether, reroute the crankcase breather hose to an independent breather filter instead of to the airbox.



While putting the tops on, the long needle-nose pliers comes in handy. This is carburetor number 3, the one that has the most stuff around it. Click on the image to enlarge it.

Here we see the air cut valve before its cover goes back on. Note that the o-ring must be in place. Hold it in place with a touch of grease. If you would like to eliminate the air cut valve system, merely replace the o-ring with a circular punched out piece of inner tube or similar thick rubber. Click on this image to enlarge it. Don't forget the spring, too!



Unless you just like doing this frequently, consider some preventative maintenance. Believe it or not, just draining the float bowls each season does absolutely nothing. On the other hand, this product, Sta-Bil, when used according to directions, will preserve the fuel for up to two years. It may prevent the carbs from ever gumming up again. It works. Click on the image to enlarge it. Available at most auto parts stores, as well as Honda and Kawasaki dealerships by part number.

A more thorough treatment of the job, this book is in its fourth edition, and is now over 55 pages. Now includes o-ring replacement, carburetor removal and replacement, QR and more. Rebuilding the CBX1000 Carbuetor takes the reader step by step through cleaning and rebuiilding a set of Honda CBX six cylinder carburetors. With the recent addition of how to replace the casting (body) o-rings, this is more a rebuild book than one just on cleaning. Included is how to remove and replace the carbs, how to get those pesky idle jets clean, detail about the various circuits, and eliminating the troublesome air cut valve. Also, how to adjust the float level, dealing with common carburetor issues, and even how to blueprint the accelerator pump. And now, replacing the carburetor body o-rings! With this page count, the best value of all my books! If you have a four cylinder instead of a six cylinder, here's another book for you to look at. The CBX book is 8 1/2" by 11", 50+ pages, and contains almost 200 clear illustrations, most of them close-ups. Also included are full-page diagrams of complex circuits. The booklet is just $34.95 plus 6.45 domestic, $23.95 Canada, $33.95 everywhere else (new USPS rates for 2016), for fast USPS Priority Mail shipping. Combined shipping on multiple purchases. PayPal will automatically adjust the shipping amount when you check out. Can be on your doorstep in just 3~4 days. Check or money order okay also. Contact me or go here for more information.

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