Hi all , I replaced carb. inlet rubbers and now my nc30 doesn`t pass 8k on the rev counter , i`m running 106# main jets and air screws are 1 and 1/4 turns out ,before i replaced them she was running like a bat outa hell but i had idling problems ,i then replaced the rubbers and the idling was fine but now she doesn`t run that well anymore and there is spark front and rear over 5k so i ruled out the speedo problem, so what did i miss??

I'm not an expert on NC30s, but 106 sounds waaaaaaaaaay too small for mains!

Quote from the all signing, all dancing carb/jetting thread:

"Standard jet sizes are: 1989 Jap model (4 x 110), all other year Jap models (2 x 115f, 2x 118r), all UK bikes (2 x 120f, 2 x 122r). "

That`s what other ppl have said to but my question is why did it run fine before and now that there are no air leaks it doesn`t run so well?

Probably a very naive suggestion, but maybe in this instance the extra air was actually helping? I really don't know...

I'm assuming there were no restrictors in the old rubbers.
You sure it's not an nc35 carb?

nope , STD. nc30 carbs

106 is too small for a stock 35 too.

SilverSurfer wrote:Hi all , I replaced carb. inlet rubbers and now my nc30 doesn`t pass 8k on the rev counter , i`m running 106# main jets and air screws are 1 and 1/4 turns out ,before i replaced them she was running like a bat outa hell but i had idling problems ,i then replaced the rubbers and the idling was fine but now she doesn`t run that well anymore and there is spark front and rear over 5k so i ruled out the speedo problem, so what did i miss??

Your in SA so no idea what your altitude is like.

Lets just go on what you have said that BEFORE you took it apart it was fine with the same jetting right?

Then I have to say you didn't put it togeher properly!

Common things.

Fuel vaccum line... split / bent / cracked.. will collapse at high RPM and starve fuel and ruin runnign of bike.
Bad fitting carbs / air / airbox / snorkel: will ruin bike at speed.

some other air leak.

did you check valve clearances and balance carbs? this is most often cause of shitty idle

Hadn't spotted the location. I know nothing about the effect of altitude on jetting, all I know is that higher altitude means less oxygen in the same volume of air. I would have assumed thinner air meant bigger jets so that you'd get more air and fuel in, but also if 106 are being run, I guess that actual situation is smaller jets so that less fuel is given per unit volume as there's less oxygen to burn it in?

Hi guys i found the problem , all i did was remove the air filter and put some mesh on the snorkel to prevent dirt from entering carbs and now it goes redline in all gears and power band kick`s like crazy .
So basically the air filter is/was stuffed and not enough air was coming in.