NC30 De-restriction Procedure

[This page is still a work in progress. Please check back later for updates...(and the photos, of course)]

Introduction

NC30s manufactured for road use in Japan came equipped with an electronic speed restriction device in the speedometer that interferes with the bike's ignition when the speedometer reads approximately 180kph or higher. The effect is similar to hitting a rev-limiter, and, in fact, the same thing occurs on a stock NC30 when rpms exceed approximately 14,500. 180kph is approximately 112mph—a respectable (not to mention illegal) speed on the public highways in nearly all countries and jurisdictions—but if you have to ask why the NC30 should be de-restricted, you're probably logged-on to the wrong Web site, pal...<g>

Electromechanical Restriction

The speedo restriction works as follows: Behind the speedometer dial, there is a piece of flat metal attached to the speedo pointer that passes between two magnetic sensors (mounted on a small circuit board) when the pointer rotates past 180kph. This event triggers circuitry in the bike's ignition control unit ("ICU") that cuts the spark to the cylinders as long as the speedo pointer remains above 180kph (it won't for long—unless you're riding down a really big hill...).

There are several ways to defeat this rather sorry attempt to hobble the NC30 and stifle its natural yearning for freedom. The first is to simply disconnect the speedometer cable: no speedomer; no speed restriction. However, the speedometer is generally considered a useful device for a street-ridden motorbike, so more elaborate measures are generally undertaken.

De-restriction Devices

De-restriction devices that plug into the bike's wiring harness, either behind the speedometer or at the ICU under the tail fairing, are available from many sources and cost about £50 (approx. $85). These are commonly referred to as "black boxes" or "M-Max boxes." (The latter comes from the name of the Japanese manufacturer of one of the most common de-restriction boxes, M-Max Corporation.) As the NC30 has long been raced in Japan and elsewhere, there is also a special (not to mention expensive—around £300 new) HRC ECU that—among other things—omits the speed restriction circuitry (not that many race bikes use speedomters, but, whatever) (Note: this is the NC35 version, but the NC30 unit is similar). Fitting one of these devices is certainly the easiest way to de-restrict an NC30, but it is rumored that these devices also remove or raise the rev limiter (this has not been confirmed, nor would it necessarily be undesirable, but...).

Doing it Yourself

Certainly the most satisfying (and least expensive) way to de-restrict an NC30, however, is to do it yourself, as described in the following procedure:

The first step is to remove the NC30 speedometer from the bike; this is most easily done with the top fairing removed:

Once you have disconnected the speedo cable, unplugged the wiring and removed the speedo from the bike, you can take it apart. Unlike the NC30 tachometer, the speedometer comes apart easily (and goes back together easily!), but you need to first remove the tiny grub screw from the end of the trip odometer reset knob:

Next, remove the screws holding the speedo housing together, and, when you take it apart, you will see the small circuit board and the metal plate on the speedo pointer so eloquently described above:

Now you have a couple of choices: You can attack the metal piece and bend it or remove it from the speedo pointer, or you can remove the small circuit board from its position in the speedo housing. VSource.org favors the latter method, as it is less likely to cause damage to the delicate speedo pointer mechanism. If the circuit board is relocated outside of the speedo housing, care must be taken to seal it against water damage—but be sure to keep it plugged into the bike's wiring harness, or the ECU will switch into "limp-home mode" and the engine will run only on two cylinders.

Finally, put everything back together and go for a test-ride! (on a closed course and only with a professional rider on board, of course)

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