South West Bikers | Motorcycle Forum

Anybody had experience of this ? Does this sound correct ?

The restriction is controlled by a sensor in the speedo, which can be circumvented fairly easily.

First remove the speedo assembly - two bolts, speedo cable and the two connector blocks.

Remove the cover from the speedo - Lots of black posidrive screws plus the odometer knob. This is held in place by a tiny posidrive screw in the end, which is normal ......

Remove the speedo unit - undo 4 silver posidrive screws at the rear of the assembly.

You should now be able to see the sensor. It is a cam shaped disc attached to the speedo drive, which makes contact with a metal strip (you will see its connected to one of the two wires that come in through the back of the speedo) at the magic 180 klick mark. All one needs to do is bend the strip out a tad so it doesnt make contact with the disc and snap ..... the bike is derestricted.

You will also see that the two wires entering the speedo are connected together by a resistor. This is just to tell the bikes electrics if the sensor has been disconnected, and if it is not in the circuit causes the bike to misfire above 5500 rpm.

think the best person to ask mav is gavin, i think he had one of those

Thats how it's done, I never did mine as I got a 'black' box which runs inline with the CDI unit. You can also buy a mechanical KPH>MPH converter, this will bypass the restrictions (unless you do 180MPH )

You can buy this black box from: http://www.400greybike.co.uk/TheShop.asp (Check that it works with the NC24 tho!)

Best bet would be to get over to 400greybike.co.uk and ask on the forum, however the NC24 isnt the most common of bikes so theres not a huge amount of info on them.

my brother bought some black box for his, which was fixed near the clocks, i shall ask him wat he did. think this could be he same thing gav's on about.

In the Japanese market, 400cc motorcycles were once restricted by top speed, but these restrictions can be removed through various means, including the fitting of an ignition "black box". Later models were restricted by power, with 59 PS (44 kW) being the limit for 400cc motorcycles, but this kind of restriction generally requires much more difficult power-increasing techniques to circumvent.

The "black box" upgrade for grey import bikes does not increase engine output, it simply removes the speed restriction of 180kmh. This is triggered by a sensor via a tab attached to the speedo needle on the back of the speedometer which cuts ignition to the rear two cylinders. The black box is an expensive option compared to simply bending the metal tab out of the way or soldering a 2.2KΩ resistor into the circuit (which is all an "black box" has in it anyway).

Think i will skip the "black" box ...

Actually, thinking about it. Are you actually sure it's restricted? I didnt think they started the whole 180KPH restriction thing until 1989, Kellys 1988 NC23 was never restricted.

At 112MPH it should start jolting like a kangaroo.

one way to find out, i found mine would hit it quite hard and it would kill the engine for a split second, not nice thing to have happen at 112mph!

I'm not a mechanic.


My mates nc21 had washers between the carbs and the cylinders.

could see them by taking the air box top off and opening the throttle.

Jonny, thats a 33 bhp restriction, they are trying to remove the 180 kmph top speed restriction.

Sorry.

how much more would you expect in top speed than 112 mph?

I would recommend dropping the engine out and swapping it for the one in that blue & white thing you got in the garden

Tom L wrote:how much more would you expect in top speed than 112 mph?

On behalf of Leroy... whatever I can get... even 2mph gives you a bigger smile...

Dave wrote:I would recommend dropping the engine out and swapping it for the one in that blue & white thing you got in the garden

On behalf of me... F**k off...

Maver-Nick wrote:

Tom L wrote:how much more would you expect in top speed than 112 mph?

On behalf of Leroy... whatever I can get... even 2mph gives you a bigger smile...

Dave wrote:I would recommend dropping the engine out and swapping it for the one in that blue & white thing you got in the garden

On behalf of me... F**k off...

Swap bikes Nick as you might be able to get a 400 around the corners

Gsxrage wrote:Swap bikes Nick as you might be able to get a 400 around the corners

I knew I was setting myself up for that one Age... ya Barsteward...
Have you seen the 'Saddam' post ?... that'll be you by your balls if you're not careful...