Don't neglect the idle jets
Many late model Keihin motorcycle have pressed-in idle jets. It is imperative that those jets be removed for cleaning, and cleaning not only the jets themselves but the intricate passages underneath. There are some good and some not so good ways of going about removing these jets, and if done properly they are reusable. Don't use a screw extractor! On VB carbs, drilling and tapping is needed to extract them, which produces chips and debris. Therefore, the carbs must be thoroughly flushed afterward, so they should be to unracked for proper cleaning out of the debris. In addition, those jets should be "sized", that is, their holes gauged for proper size. A lot of folks drill them larger--don't--and aftermarket replacement idle jets are universally oversize.

Don't overlook the primary main tubes
Early VB carbs have what is called a primary main circuit. This circuit includes a tube that is difficult in many cases to remove. Many have resorted to using screw extractors but this is not a recommended method and not the one used by professional rebuilders. Beware of the rebuilder who shows a lack of understanding in this area, and look out for those who completely give up and neglect to remove this part during their rebuild. The best way to temove a stuck primary tube is to drill it out. There are quality replacements on the aftermarket.

Don't ignore the air cutoff valves
The air cutoff circuit is not an emissions part, and is not even a necessary circuit. It was added-on through politics more than anything else. Remove the aircut diaphragms before beginning cleaning work on your carbs, or make sure the person doing the rebuilding does. The aircut valves must be disassembled during a rebuild because the circuit is part of the idle circuit, the most critical circuit in any rebuild due to its small size and high complexity. The valves can be bypassed, which is a good thing to do.

Don't use aftermarket float valves
Using badly manufactured aftermarket float valves continues to be one of the most serious mistakes a rebuilder can make, whether a do-it-yourselfer or pro. The limited availability of factory parts and their high cost drives many to the aftermarket, but that is always a very poor choice. Aftermarket float valves seldom seal as well as the original for one thing, the very reason you are replacing the valves. Resist the temptation to go with the much less expensive aftermarket valves for these carbs.

Don't abrasive clean float valve seats
In most cases float valve seats are non-maintenance. On some VB series (early Honda DOHC four, for example), they are even pressed-in, making servicing them a moot point. Careful cleaning with carb aerosol and a Q-Tip is all they need and should get. Under no circumstances should the seats be burnished or polished, as this has the potential for changing their internal shape. The pressed-in seats can be replaced, but this is a job for someone with machinist's skills. Threaded aftermarket seats often include poorly made filter screens that look quite different from stock, don't fit as tightly and deteriotate almost immediately. Also watch out for sealing washers that are thinner than stock, quite flimsy in fact, as these wear quickly, interfere with the filter screens, and alter float height setting.

Don't abrade or polish anything
The only parts that should be sanded or polished on a carburetor are the beauty covers. That is, the tops or bottoms. That's it. Not the slides or slide bores, not the butterflies (!), and not the float valve seats (see above). These things are manufactured to a high tolerance. Do you take apart your watch and start sanding on things...?

Don't make epoxy repairs
It's a rare epoxy that is resistant to gasoline. If someone has done epoxy repairs to your carburetors, or is planning to--don't. And when it comes to the ubiquitous JB Weld (a common epoxy), consider this. Readily available carb cleaning chemicals dissolve it. That's right. Dissolve. As in not a trace. There are much more professional ways to do these kinds of repairs, including welding, which is common among carburetor professionals.

Don't use stainless steel screws
Carburetor castings are made of an aluminum alloy that is not very "clean"--there is a lot of iron and zinc in the mix, especially in pre-1980 Honda carbs. The metal is already ripe for electrolytic action, don't make things worse by adding stainless steel screws. Faster than you can say "electrolysis," those screws will begin bonding to the casting, and the next time they are removed they will take aluminum with them, tearing up the threads in the carburetor. Sure, those stainless screws are pretty, but at what price? And yes, a dab of grease or antiseize on the screw threads can help, but overall the use of stainless screws just isn't good practice. Worse yet is most of these screws are socket head (we call them Allen head, but that is actually a trade name like Kleenex). Allen screws permit too much torque to be applied to the threads, especially if using a typical Allen wrench. If you must use Allen screws, at least avoid the L-shaped Allen wrench and use instead a screwdriver type. You can tell an inexperienced carb rebuilder by his use of these kinds of screws.

Don't mangle your throttle plates
Especially if the carbs have been unracked during the rebuild, which is in most cases a given, the throttles will need to be resynced, and this should start with a bench sync. The accepted method is to open one throttle until the butterfly just uncovers or bisects one of the carb's bypass ports. Under no circumstanes should anything be drug under the throttle butterfly! Not only is this a method for a different type of carburetor altogether, it is harmful to the butterflies, which are finely machined and very soft aluminum. A few rebuilders synch and test your carbs on a running engine, and that's a pretty good thing to do. But it's good more from the standpoint of the rebuilder catching his own errors, such as leaks, than for other reasons. Working well on a test engine in no way guarantees your carbs will work equally well on yours. All conscientious rebuilders do final adjustments on your carbs in many ways. Synch, leaks, accelerator pump action, fast idle mechanism, etc.

Don't ignore your pilot screws
Being a longtime, factory-trained, in-the-trenches for years seasoned Honda mechanic, I am saddened each time I start a rebuild on a set of carbs and find that they still have their factory-installed idle mixture screw limiting parts on them. Imagine it! In many cases fifty years without adequate maintenence! What kind of shop would allow this? What kind of owner? Whatever folks are being told on Internet forums, the limiting covers and stop flags on idle mixture screws are supposed to have been removed, if not during the initial setup, then at least by the time of the first maintenance service.

Don't use thread locker
There is only one place anaerobic thread locker such as the ubiquitous Loctite belongs on a carburetor, and that is the throttle plate and choke plate screws, if applicable to your model of carburetor. But beware, even here, the unprofessional messes up. Never use high strength thread locker on those tiny screws. Do you really like the idea of using a torch on your carburetors?

Don't mess with the throttle shafts
In most cases, carb throttle shafts should not be removed. This operation is too delicate for most to fool with and is very seldom necessary. Alignment of the throttle plates can be very tricky. The felt seals most carbs have on their throttle shafts will live happily a very long time as long as folks don't mess with them.

Don't worry about the felt seals
Speaking of those seals, they are for dust, not vaccum. Therefore, an engine running problem is not going to be solved by replacing them. Anyone who tells you otherwise is ignorant. Honda CV carbs have bronze bushes. Not in your lifetime are these going to be worn out by dust. Leave the felt seals alone.

Don't use crap fuel hose
In my book, the presence of plastic fuel line on a carburetor is a sign of unprofessionalism. That stuff is so crappy it shouldn't need to be explained, it should be obvious. Only if I were doing a concourse level resto on an old Brit or Italian bike would I even consider using that stuff, and then only for originality's sake. And worm drive type hose clamps do not belong on your carburetors. If your hose needs that kind of clamp, it is poor quality and/or the wrong size.

Don't use carb rebuild kits
Carburetor rebuild kits are junk and another way in which would-be rebuilders drop the ball deeply into the weeds. Keyster, Napco, BikeMaster, Sabre Cycle, or K&L rebuild kits--they're all trash. It's hard to think of a worse thing to do to your carburetors. Carb kits contain the aforementioned float valves that either don't work at all or deteriorate very quickly. Sure, factory valves are expensive, as in four times the cost of aftermarket. In this instance however you really do get what you pay for. Also, carburetor kits invariably include a lot of cheaply-made brass (metering) parts. There are a number of problems with this. You very rarely need to replace jets in a carb rebuild. Worse, they usually made to specs that vary from stock. And worst of all, being made of brass they will wear much faster than the original materials on U.S.-spec Keihins made after about 1977.

Don't use carb jet kits
Carburetor jetting kits exist for just one reason: people would rather throw fuel at a problem rather than diagosing and really solving it. It's true. As your machine wears carburetion leans out. This is because lower compression makes the engine less efficiently use fuel. Gradual changes in adjustment--valve clearances for example--can do the same thing. Commit to regular proper maintenance and you will find you do not need a jetting kit. Even in modified engines which require carburetor changes, these modifications are best carried out using factory parts.

Don't rely on abrasive blasting for cleaning
Abrasive blasting is a good way to renew the appearance of carburetors. But too many--including folks who rebuild carbs for others--regard it as a substitute for actual carburetor cleaning. It's not. A carburetor is a lot like an ant farm. Remember those? You could see what normally wasn't visible, all the tracks the ants made in the earth. Carburetors have those kinds of passages also. They are not cleaned by abrasive blasting, and in fact they are at risk of clogging up if care isn't taken. Where carburetors are concerned, blasting is a texture improving process, not a cleaning process.

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