Model Info Service Info Performance Accessories
Sources/Links Sights & Sounds VF/VFR FAQ ? Home

NC30 De-restriction Procedure

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


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...).

Speedo Guts w/Restrictor

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: Home Copyright © 1999-2005