need help despirately with my nc30, ongoing problem for ages

[Danzio]

Ok so i took my vfr for a ride today and its been great weather so i thourght id open it up in the country side abit...

was fine around town through the gears up to 50-60mph but as soon as i took it to about 7 1/2 - 8 thousand rpm it starts to make a really growly noise from the engine, the power which normally helped me hurtle forward feels much more reduces and there is a distinct vibration.

the bike itself is in good working order, fine up till those rpm and it will go to them, all the way to 14500rpm, but its feels like its lost alot of power...

its only just started but need some advice on what to do here, sounds smooth to 8000rpm when it usually picks up but then afterwards dosnt deliver the power ive known it to, sounds more like a v-twin than a four!


anyways heres a good description,

get to 8000rpm, wind it on and its feels like it loses power, sounds like a vtwin, little more vibration and a different exhaust note...

as if i was running out of petrol, but im not, ive checked that!

is it still restricted somewhere? this would be my first guess, either that or a fuelling problem as it wont go past 110mph 180kph.....

im sure it wont be valves, or the carbs as they've just all been serviced and were in good nick anyway.

the bikes done 17300 miles..

UPDATE: i posted this on bikechatforums to little avail you guys are my only hope!

a better description would be to say the bike revs to 14500 in the first 4 gears but struggles in 5th and 6th.. feels like a cold two stroke after 7000rpm gets to 14500 but with much less pull and power.

now ive checked the ht leads and spark plugs all which are fine, as is my battery, fully charged, alti's fine as is the reg/rec... im stumped, is it a fuelling problem? when i pull the throttle fully back it does sound like the point before you go onto reserve when you pull back the throttle and it sounds hollow and gaping...not sure anyone got expiriance with this...?

help me!

[CMSMJ1]

What speedo readings you getting when this happens?
Check your vacuum pipe has no cracks or splits- it might be collapsing when hot and starving the fuel flow.

Have you changed anything at all withthe airbox/filter/carbs?

My 20p bet for the money winner is that you have cut the front airbox flap off and at speed it is just not fuelling right because of it...lets have a look!!

Welcome - this is the place to be for anything NC related...you'll get this sorted on here I am sure of it

[Danzio]

ive had the tank etc off to check all the plugs. aint checked anything to do with the carbs.

is the vacuum pipe the thin pipe with the metal connector which (when sucked) releases fuel from the tank to the fuel line? if so this was persished to we reattatched it cutting the persished bit off. like i said the engine runs champion, just when i want to go anywhere(fast!) it bogs down loads and im certain it'll be the fuelling...

and whats this about the airbox? ive never taken anything off it and to my understanding (using diagrams from the service manual) its all intact and original..?

saying that, the problem used to happen, just slightly, as in, get to say.. 120mph and hit a flat spot, then it would shoot back up again..? weird! dont know whats going on here as im pretty new to these bikes.

[Danzio]

oh and thanks for the warm welcome. much appreciated

[CMSMJ1]

No worries man - I'd be chekcing your vacuum hose - if ncessary I'd get a new on.

Sounds like starvation to me or poor fuelling.

How long have you had it and when did it start?

Also - they're restricted to 112mph and this cuts the spark to 2 cylinders. It can be bypassed and the quickest way is to unscrew the speedo cable IMO - there are other ways, but not as cheap and easy to do in 2 minutes.

The go rag it as fast as it goes and it will hopefully top out (on a private road..or somewhere safe)

the airbox - it has a flap on the front of it - often gets chopped off and this causes fuelling issues..

[Psychosomatic88]

I agree with CMSMJ1 here.

Also on the airbox frontier, check that the removable scoop is there and located well. This is the part on the airbox lid, and guides the air into the 'box.

[Danzio]

I've had the bike about 2 months now, but its had no real history of bad stuff! ive got all the service receipts for work done, all the mot certs, import papers the lot. its been well looked after and only has 17000 miles on the clock which when looking at how clean the bike is and backed up by service and mot certs is a dead cert.

just can't understand why when you buy a bike and get excited to ride it...something goes wrong..sods law maybe..?


ah i see, yeah sounds like fuelling to me. im not sure it would be running this rough standard...even with a 112mph speed restriction. fuelling is my guess too...

ill check the vacuum hose, as im pretty certain that under higher revs..(more stress) it could collapse leading to poor fuel delivery no?

hmm funny problem but ill try unscrewing the speedo see what happens, not sure that would work however as its been maxed out before...on a...err...private road...ofcourse..

i'll have a check this lunch time as i have my bike with me at work. like i said cms, its fine when using little throttle, ie: quarter to half :)

thanks for the help so far mate. oh yeah and the flap on airbox..rubber yes? please explain why people cut it off?

thank you for your time, its much appreciated

EDIT: I'll go up to my local bike shops on westgate road as one of the owners of the shop owns an nc 30 so ill see if i can turn anything up. in the mean time more comments on this problem are very helpful. cheers guys :)

[dbanbery]

check your CDI plug isnt shorting out on the metal hanger bit. when i fitted my restrictor box i noticed that the cable wasnt in the metal hanger. so i fitted it like it should. then the next time i took it out i started having intermittant issues with running on 2 cylinders, loss of power, stalling etc. its a long shot, but worth a look.

[Danzio]

i'll check that tonight yeah.

you guys are great at replying fast and its really appreciated. thanks a bunch.

i'll give the old girl a working over tonight after ive been to the gym and given myself a good working over

in the mean time any more info would be great, plus ill post up tonight after i've had a tinker on...hopefully i'll get some replys...unless all you guys are on the drink!

speak soon fella's, cheers.

[dbanbery]

.

i'll give the old girl a working over tonight after ive been to the gym and given myself a good working over

and youre going to check the bike out before? or after?

LOL!