® Sixteen things every Honda CBX owner
should know

The Honda CBX is a very special motorcycle. At over 40 years old it is far from the fastest or best performing. Even at its debut it enjoyed king-of-the-hill quarter-mile status only until the Suzuki knocked it off its tenuous throne merely a few months later. Heck, with its origin in a 1950s NSU design its multivalve multi-cam engine was already old tech before it was even produced. So no one has illusions, not then and certainly not now. And heavy? And wide? And a 19-inch front wheel? But with all those antiquated characteristics, there is still an allure, a captivating finesse, special character, and visceral thrill that is rare and hardly matched in today's motorbike offerings. I especially appreciate the CBX engine's unique DNA, a sort of amalgamation of vintage European technological brashness with practical, durable Japanese engineering. It's very much a Lamborghini with Asian foster parents. It's a neat bike, very possibly my all-time favorite, both to own and ride as well as to service and rebuild. However, in this day of low-maintenance vehicles this attention-demanding machine is an anachronism, a thing unexpected and unfamiliar. And all too often, sadly neglected. Thus I find the following handful of things important enough to encourage every CBX owner to put them on a list of things to know.

1 First--and this really is first--the number one shortcoming found in any used CBX is cylinder compression. And it matters. This is in fact the CBX's Achilles heel. Partly, this is due to unusually fast cylinder wear due to this engine's uniquely high heat. But much more is due to valve issues. Honda used soft valves in the CBX. Even very low-mile engines have already lost a significant percentage of their compression. In fact, 120-130 psi is common, about a thirty percent loss. Bikes with only 7,000 miles on them suffer the effects, and valve wear is extreme by just 15,000-miles. And all because of cheap valves, for which quality long-lasting aftermarket replacements are available and strongly recommended.

2  Second in importance, the CBX's carburetors have circuits that are really tiny and precise, thus they are prone to varnishing up very easily. If the machine sits three to four weeks, that's enough to plug things up. You simply must keep Sta-Bil fuel stabilizer in them at all times, round the clock. Unless you think nothing of having them expensively rebuilt each riding season. Sta-Bil really works. Use it.

3  Third, if you value your carburetors, stay away from jet kits. They are Bandaid fixes even on those machines for which they are relatively suitable. Actually, they make up for other issues on those machines that should themselves be addressed. But on the CBX, they have no redeeming value. Do not put a Dynojet kit in your carburetors. There is no carb tuning/rejetting that cannot be, and isn't best, done using factory parts. Experienced professional rebuilders remove Dynojet kits from CBX carbs every day. There is a reason.

4  Fourth, due to the CBX's hot-running engine, on warm days the carburetor's float bowls can evaporate as much as half their volume in just a few hours of sitting after a long ride. Be aware of this when starting the bike later, as it means the carburetor bowls have to refill before the engine will start. It is not good practice to simply wail away on the starter hoping the bike will eventually start.

5  Fifth, on 80 and later models the above issue is exacerbated by the vacuum fuel shutoff valve which will not allow fuel to flow until the engine is cranking over during starting. So even more time needs to be allowed. You can reduce the strain on starter motor and battery as well as the potential for spark plug fouling by clamping the vacuum hose during the first few seconds of cranking (use a hemosat), then turning off the key and waiting while the fuel flows on its own into the float bowls. Give it at least five minutes. It takes a while to load up 300 milliliters of fuel.

6  Sixth, still about the carbs. Draining them. This is a frequent need on a CBX. Almost no one rides a CBX daily. In addition to running Sta-Bil full-time, if your rides are more than three weeks apart the carburetors must be drained. This is easiest if the overflow hoses are permanently removed.

7  Seventh, there is an even more important reason to remove the overflow hoses on a 79 model. This will prevent the infamous cylinder hydrolock.

8  Eighth, the CBX alternator has got a bad rap. It's not a pile, contrary to what many believe. Once set up properly, it, like the brakes, is trouble-free and a good performer. There is nothing wrong with the Denso-based alternator conversions. They're fine. But they are completely unnecessary. The stock alternator is powerful enough and durable enough to do its job. Even the all-too common and potentially expensive issue of excessively-worn drive disks is cheaply and instantly overcome.

9  Ninth, as with every vintage bike, the CBX's electrical connectors are of a design whose terminals are exposed to the ravages of the elements, thus requiring frequent inspection and ultimate rehabilitation. Expect corrosion and melting of the plugs. The good news is, all the needed parts are available, even from Honda, and getting after this has the potential of improving electrical performance. Done right the repair will never have to be done a second time. And it really needs doing.

10  Tenth, the state of the brakes on every CBX that enters my shop is inevitably disappointing. But they needn't be. While typical Honda 70-80s tech, meaning single-action, collet design as in virtually every mass-produced passenger car and thus relatively low-performance, the little-known truth is, the stock brakes -- that is, with almost all stock parts -- can actually be quite good. All it takes is a little knowledgable attention. I spend nearly as much time on the brakes as I do the engine on every CBX I fettle, with the biggest problem being improper assembly and the use of really bad aftermarket parts. High performance brakes aren't the answer. Getting after the brakes you already have is.

11  Eleventh, the ignition system demands attention. Are you aware that timing the CBX ignition requires the exact same setup as was necessary to time a pushrod Brit ignition, a specially-modified 6-inch degree wheel, to begin with? Even with a Dyna. By the way, the Dyna ignition system available for the CBX is a good product, but one that is usually incorrectly installed. You really don't want to ride an already hot running CBX around with its ignition overadvanced by 10 degrees. Moreover, the CBX's transistor boxes, or "igniters" as many call them, are all going bad. In a recent year, two out of three CBXs in my shop had melted igniters. And unfortunately, the expensive aftermarket replacements have been proven to be poor quality.

12  Twelfth, with the engine a stressed member of the frame, it is important to properly install and tighten the engine hangers, some of which have to be removed for each valve adjustment, and all of which are removed each time the carburetors are. Almost every CBX that makes its way to me has had someone install them incorrectly -- often stripping the threads in the frame -- or tighten them in the wrong order, which also promotes damage. What's worse is aftermarket hangers. I have yet to see one that is made correctly. Really, you ask? Yes. What aftermarket hanger makers fail to do is to replicate the stock hanger's offset. The original main engine hangers have an offset between the top and the bottom. All the aftermarket ones I have worked with are absent this offset, requiring shimming the bottom with washers to properly create it, which I have had to do many times. Failing to do so results in the hangers being bolted up crooked.

13  Thirteenth, nothing is cheap on a CBX. An engine top end rebuild done professionally and correctly will cost you between $12,000and $15,000. And if it hasn't been done yet (and in many cases even if it has), it needs to be.

14  Fourteenth, the aftermarket is not the friend of the CBX owner. Never has been with any vintage Honda. But with the CBX it is worse. The CBX is a magnet for all that is wrong with that part of the industry. There is very little there that is good and an awful lot that is not. The experienced mechanic will know the difference.

15  Fifteenth, don't use non-OEM valve cover gaskets and bolt seals. Their inferior rubber material overcompresses and leads to oil leaks. The factory ones are still available.

16  Sixteenth, the online voltmeter is not well understood. First, volts are not the best way to monitor a charging system. Charge is current, not volts. Second, even if it were, the voltmeter does a lousy job of being accurate since it is wired some distance from the battery, with the result a 1-2 volt disparity. Third, the CBX's charging system like all of Honda's big bike systems from the mid 1970s does not charge its battery at idle. Certainly you have noticed this. At idle the voltmeter will always read less than 12v, even with a perfect system. At 1700 rpm the voltmeter will read over 12v. Two faults can be reliably indicated by the voltmeter. Worn brushes and a slipping drive clutch. Deeper problems are best troubleshooted.

I hope this has been instructive and useful. The CBX is a wonderful bike. I had mine for over 50,000 miles. But I have actually discouraged more than one individual from acquiring one when I felt they would be challenged by the inevitable needs previously-owned machines tend to have due to neglect and ignorance. If you are a new owner, or are about to be, see my article on the general costly and labor-intensive nature of putting a used CBX in shape after purchasing.

Further reading:
The challenging Honda CBX
CBX myths
Real issues

Last updated January 2023
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