Sickly nc

[edwar65]

Hi, I wonder if anyone can offer any help with my poorly nc30.
Recently took out bike as it hadn't been ridden for approx 6 weeks.
Once bike was warm after a few miles, revved it through the gears up to around 12000 rpm and then it suddenly developed what I thought feeled like a lack of fuel, sort of misfire under load.
I re-fuelled bike but the problem is still there, basically if I try and rev it past 6 thou it feels like it's running on 3 cylinders, this is also true if I put it into higher gears and try to accelerate the engine again feels as though it's running as above???
I checked the exhausts and the rear riders right cylinder exhaust definitely felt a touch cooler than the others?
I took out the spark plug and it looked an ok colour and was not wet with oil or fuel, I'm wondering whether it could be a duff plug/lead, but I'm getting good sparking to frame turning over engine with plug against framework?? I have no spare plugs to try and don't want to throw money at new plugs in case it's not them at fault.
Any suggestions/guidance would be most appreciated!!
Thanks.

[Morespeedvicar]

Hi, just wondered if your speedo is still working ok? Other things to maybe look for are a cracked vacuum line to the fuel tap or maybe a sticky needle valve in the carb?
You could take spark plugs out clean them and swap them round keeping note of were you put the suspect one.
Hope it helps

[magg]

Start engine and monitor battery voltage while running above 5000 rpm.

[edwar65]

Thanks for reply guys, speedo working fine and vacuum pipe ok. Ruling out jet problems,what sort of volts should I be getting at 5000 rpm and I assume this should be constant??
Cheers.

[magg]

No more than 15.

[edwar65]

Checked voltage @5000rpm reading 13.95v. This is bang on for rectifier output.
Any other suggestionsuggestions? ??

[magg]

IMHO voltage a little low but better than >15 volts. Is bike a Japanese grey import?

[edwar65]

Yes it's a 91/92 model according to frame/engine no,s.
Thanks.

[magg]

As alluded to by morespeedvicar, Japanese bikes have speed restriction system that operates via the speed and cuts rear cylinders above 130km/h. If the restrictor becomes disconnected or faulty the cylinder cutting begins at start up. Maybe this is your problem.

[Malc]

The cut out occurs at 180km/h ordinarily. If I remember correct, when the restrictor is in some way faulty, the engine will start to stutter at 5500rpm in every gear.