® The CBX1000 super tune


I have been servicing the CBX1000 since its introduction. For this venerable machine I offer a service I call a "super tune". It consists of all the things that through long experience I have found are needed to get the bike back to the factory-intended state of running excellence after nearly fifty years of inadequate and inexpert attention. Little of this service is concerned with things outside of the engine and its support systems, though I always create an observations document for the customer in which I list issues with such things as brakes, chassis, and electrical. They're always needed, though not intended to be included in the super tune. Following is an outline of what the CBX super tune consists of.

  1. First I visually inspect the machine. Almost a half-century of working with Honda's CBX has enabled me to make conclusions about the kind of care and attention the bike on my lift has received up to the present, and this directs my thinking on the systems I'll be optimizing as I proceed. I have to say, the CBX is one of the most neglected motorcycles of its era. Most of the ones I see are in really rough shape. More or less "clusters", to put it bluntly.

  2. A compression test is the first step. There is no point in investing time and money in a machine that has a seriously worn engine. And unfortunately, most CBXs are in fact seriously worn. They are especially prone to having low cylinder compression due to the soft valves Honda put in this engine. This seriously impairs compression by just 15,000 miles. Though the bike left the factory with 170 psi, it is rare for a non-repaired CBX to exhibit more than 140, and usually less, due to both this valve problem and due to the engine's extremely fast-wearing cylinders--the factory documented an engine temperature of nearly 500 F. I won't do a super tune on an engine that has low compression. So this needs to be determined right away. The compression test usually requires the battery to be recharged halfway through the testing process, affording me also a good look at the battery and inspection of the starter motor's condition. More often than not it is a cheapo battery, not one of the better brands. Additionally, a bad neutral switch is known to cause electrical conductivity problems with the electric starter. All of this observation and a lot more is part of a CBX super tune.

  3. Ninety-nine times out of a hundred, super tunes on the CBX are accompanied by a top end rebuild. I do all the machining myself on specialized equipment. I have a how-to book on the top end rebuild. Check it out. As of this writing, a CBX top end rebuild costs $12,000 minimum and often into the $15,000 range. But no CBX is treated properly without also getting suspension, brake and electrical work, which will of course push the cost higher. There are few CBXs that don't need a top end rebuild, and none that don't need a lot of other, non-related work.

  4. The compression is usually still appreciably low even on a bike that won't have its top end rebuilt. So then I remove the valve cover and perform a full complement of cylinder leakdown tests. The valve cover is removed for three reasons. One, the CBX lacks marks on the engine for positioning each cylinder at TDC (top dead center) compression. Camshaft position must therefore be observed in order to do the tests. The same is true of simple valve adjustment, by the way. The second reason I remove the cover is to estimate how much a valve adjustment will improve the engine's compression readings. It always does improve them, but it is important to know how much before I make conclusions. And three, during the leakdown tests I tap on the valve buckets so as to determine to what extend carbon buildup is affecting the compression readings. It does affect them often, leading me in most cases to do a water-tune on the cylinder head, which is part of the super tune if it is needed. The excessive carbon accumulation is due to many CBX owners unwisely using premium gas and/or fuel additives.

  5. If compression is at or above a certain minimum after the above steps, the project continues and the carburetors are removed for rebuilding. While not a particularly difficult job, the CBX carbs are just fiddly enough to get a casual rebuilder into trouble. A lot of parts, made to a price, and some design weaknesses including a pretty flimsy linkage system, make for a challenging rebuild. Obsessive attention to detail is the only way it works, in addition to a working knowledge of these carburetors. Moreover, CBX carburetors always show serious signs of neglect, rough handlng, and unfortunately inexpert prior service. The CBX intake manifolds are troublesome. Due to the engine's extreme heat, the manifolds decay prematurely. So they are closely inspected and often replaced. As of this writing the factory ones are still available and they are superior. I also find the manifolds always need their clamps repaired or replaced.

  6. Then I adjust the valves and the two cam chains. Three special techniques are employed. One, I adjust the valves to 0.007" (0.18mm). This boosts the compression and reshapes the engine's powerband, giving it a much flatter torque curve. The engine starts better, idles better, and has better throttle response as well. The second special thing is I adjust the valves in the engine's firing order. It makes a difference. Every career Honda mechanic knows the advantage this offers. I install new factory valve cover gaskets and bolt seals--the aftermarket ones are junk. The cam chains must be adjusted at the same time as the valves, because they are best adjusted manually, not with the engine running. This is the third special technique. I always find the cam chains very loose, indicating poor maintenance. You should also know the cam chains wear quickly on the CBX. They are worn out by 30,000 miles. I replace the cam chains routinely. The "A" cam chain, despite its encirculating the crankshaft, can be replaced without removing the engine from the frame and without using a cheap, Chinese cam chain. Career Honda mechanics have been doing this since the first Hy-Vo cam chain appeared on a Honda product in the late 1970s. Good cam chains are very hard to find, as Honda ran out of them a very long time ago and aftermarket substitutes are poor quality. Even the highest quality aftermarket cam chains have smaller diameter pins than do the original ones (there are two cam chains in the CBX).

  7. The cam chain tensioners are even more challenging. They also are obsolete and due to this engine's very high temperature they consistently and thoroughly fail. Of course, replacement is part of a top end rebuild, not part of a super tune.

  8. The ignition coils are inspected. CBX coils, being part of a Kettering system, frequently overheat and need replacing. The plug wires never go bad, but if suppressive wires have been fitted, I change them out for actual metal wires. This is not an option. There are three reasons. One, non-metal plug wires reduce ignition performance. Two, that performance degrades further over time. And three and most important, such wires can never be made to connect electrically as securely as metal wires. Suppressive plug wires do not belong on your Honda. "Everything affects everything". While the person to whom the Internet attributes this saying is not someone I admire (and I suspect one or another industry heavyweights whom I greatly admire actually coined the phrase), this could well be considered the professional mechanic's mantra.

  9. The spark units (ignitors) go bad on CBXs also, and the aftermarket substitutes are not very long-lived. Fitting a Dyna ignition module, while itself not such a hot idea, at least solves this failed ignitor issue, since the transistors that make up the spark units are, alternately, built into the Dyna timing module.

  10. The spark plug caps are next. They are always loose on their wires--indicating a lack of maintenance--and they are almost always degraded from their original 5K ohms to 10K or more. I nip the plug wires and install new caps. The original NGK caps are getting rare and quite expensive.

  11. The carburetors are a major and non-compromising part of a super tune. They are completely disassembled down to unracked, individual bare bodies (castings). The throttle shafts sometimes are removed, but not very often as that is necessary only when they or the throttle plates are damaged--which I see once in a while. Note also that there is no defensible reason to replace the felt seals. They are mere dust seals and ineffective even at that. After an ultrasonic bath, the carbs' circuits are individually hand-vetted. The accelerator pump system is optimized. It usually needs the most attention and ironically the CBX engine depends heavily on the accelerator pump, not working well if the accelerator pump is sub-par. The float levels are adjusted using the factory tool and method. Pretty often the float bowls need soldering or standpipe replacement. The fast idle mechanism (linkage) is almost always out of adjustment. The air filter is checked and usually replaced with the superior later pleated paper type. I don't countenance K&N air filters. Worse yet are individual air filters (pods). But if you can reconcile yourself to the resulting accelerated engine wear, they can be lived with. If pods are evident, while rebuilding the carbs I make sure they are jettted correctly for them. Individual filters necessitate a 10 main jet size increase on the CBX. If a Dynojet kit or any other kind of jetting kit is found, this is removed and proper, high quality jets and metering parts are installed, at an extra cost as these parts must necessarily come from other carburetors--they are not available from Honda. The Dynojet kit parts are about the worst things you can do to your CBX carburetors. And again, there is usually a lot wrong with CBX carburetors. They constitute a significant part of a super tune, and while they are far from the only part or even the most important part, at the same time they are very very necessary.

  12. The carbs are reinstalled. It's best to avoid doing this with ratchet straps or any other kind of force, to avoid disturbing the finely balanced assembly of the choke activation rods. Heating the manifolds helps, as does using only factory manifolds. The choke cable presents a unique difficulty on the CBX. It is almost always installed incorrectly. I have a video on this, that's how important it is.

  13. When the engine is started a careful check for oil and fuel leaks is made. Once warmed up, the carburetors are painstakingly synchronized to a standard that is three times as precise as the factory specification. Syncing CBX carbs is an art. It requires special tools, a high quality set of vacuum gauges, patience, a high CFM fan, and a high degree of skill. An exhaust gas analyzer is used to confirm the pilot screw setting and if indicated, the pilot screws are adjusted to a reading of 2.5 to 3.0 percent CO.

  14. In 2023 a CBX super tune cost $3500. Add inflation, suspension service and brakes and electrical and the ticket can easily reach $6000+. If a top end rebuild is done at the same time, the ticket is more than double this, naturally.

  15. As part of the super tune I adjust the steering bearings--they're always loose--and test the battery charging system. The clutch is frequently off on CBXs also. I am not talking about the lever clearance. That is not adjustment. Correct clutch adjustment is done at the pressure plate at the right engine cover. I lube the clutch cable at the same time. I also inspect the fuel tank and tank petcock, service the drive chain, repair the engine mounts--they're always installed wrongly and frequently damaged--inspect and air the tires, look over the suspension, and complete my observations sheet that will go to the customer.


Last updated August 2024
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