Hi, any way of the correct way to identify this issue with the the speed restrictor

Consult library section on this website for restrictor bypass mod.

Is there a process of checking out wiring, as I understand it the wiring comes out of back of speedo and goes on towards CDI unit at rear. Would it be smarter of checking plug connections and testing for continuity with a multimeter possibly??
Thanks.

Green/Blue wire from speedo plug should run to ignition control unit. Plug at speedo should have Black/Brown +12V with ignition on and Green chassis earth.

there are several ways to bypass the speed restrictor

you can remove the metal disc out the clock, this leaves the wiring in tact and only way to tell is to disassemble the clock.

you can just do the wirign speedo mod to your bike to bypass the speedo wire.

have a look at the igntion box in the back of the bike, find the blue/orange wire and black / white wire and put a scotchlock on them to connect them together.. then disconnect the 3 pin plug from the clocks.

Hi, I've never had issues with the speed restrictor before, the bike when bought has always run unrestricted so previous owner/s has done something to bypass the Japanese restriction, although i can see no obvious mods to wiring near clocks or cdi, only what looks like a blue cylindrical device at back of speedo between clock and cable? I assume this is some sort of gearbox to correct speedo from kph to mph even though speedo is in kph??
As I said bike has always run at full power until this misfire started.
Thanks.

That sound like you have a kph/mph converter on your bike. Is your speedo in kph but shows real mph?
Did you try swapping your plugs about and check carbs again?

As above, I'd try swapping the rear plugs next and see if any of the cylinders isn't firing.
After running the engine for 2-3 minutes, I spray some water on the pipes to see if all are running; the water evaporates instantly on contact when that pipe is hot.
Was your speedo reading correctly?
If the plugs all turn out to be ok and all 4 cylinders are running, check the white hexagon plastic bit at the end of your speedo cable (front sprocket end), to make sure it's not rounded off.

I'll check these things later, carbs have been stripped and look good, when I was at it I checked valve clearances etc all good.
Thanks

Finally got the bike back together and the mystery misfire has disappeared!!!?
Not sure what the fault was very strange, now running very well many thanks for all the help from the guys on the forum.
Cheers.