NC30 carby jetting - DIY guide

[Neosophist]

Hanging revs (especially around 2000) are a classic sign of an air-leak too as it's a lean symptom.

If backing the pilot screw out doesn't fix it, set the idle up to 2000 or so until you get a steady-ish RPM.

You need something flammable like carb cleaner / easy start for this next bit but work your way aroud the rubbers spraying the solution at the rubbers.. any change in RPM indicates that you have an air-leak on that rubber.

Check the carbs are seated properly and the clips are done up but not over-tightenend.

[born2ride]

just got another set of carbs as the set i had were no good. sitting 4 13 years didn't do them any favours! diaphagms were too stiff and needles in the float were shot. soaking diaphagms in petrol didn't help-2 far gone. My nc30's an import, but i think the set i now have might be off a uk speck bike? the end of the sliders are curved, they have no hoses 2 go 2 the secondary air filter and the carb bracket (where the velocity stacks are) is larger so the airbox doesnt fit. I know they aint hrc carbs. They look like a clean set of carbs on the inside, so do you reckon its best to find an airbox to fit, or run without an airbox and change the jets- if so wot sizes do u think best?

I could try swaping the brakets over if i can unseize the screws, or swap the internals over, which action do u rekon would be best? nothing ever as simple as u hope! cheers

[Cammo]

My nc30's an import, but i think the set i now have might be off a uk speck bike? the end of the sliders are curved, they have no hoses 2 go 2 the secondary air filter and the carb bracket (where the velocity stacks are) is larger so the airbox doesnt fit.

They will be nc24 carbs mate!

Best to get a set of nc30 carbs.

[born2ride]

thanx cammo, NC24 that explains it! I'm going to get this thing running if it kills me, just spoke to the guy and luckily he's got another set. look more like it in the photo! Sure ill get there in the end

[ludacris]

hey Cam, excellent write up! just wondering since there's no mention of it but is every step in the guide applicable to NC35 as well? most notably, adding the extra washer to lift the needles...i only ask as i realise that the 30 and 35 are tuned slightly different

[Cammo]

is every step in the guide applicable to NC35 as well? most notably, adding the extra washer to lift the needles...i only ask as i realise that the 30 and 35 are tuned slightly different

No mate, I wouldn't add extra washers to rvf needles. You can alter the midrange fuelling on rvf's by using hrc slide springs. The springs do a better job than washers (washers raise the needle the same height over all the slide movement - unlike the springs).

Rick Oliver sells repro hrc springs, I fitted some to my rvf carbs with good results.

The rest of the guide is fairly generic to both types of carbs, main differences being carb settings (jetting, pilot screw setting etc), looks and that the pilot screws on each set are adjusted in different directions.

[ludacris]

i had a bit of a feeling that might b the case...

ok so i'm going to do some carb and valve work for the first time while the fairings and tank are at the painter so just want to pick your brain a bit lol

1. the bike has been fitted with a TSR can and pipes so which main jet size would you recommend? read somewhere on here that 112 should do from the standard 108 (think that's the standard size according to haynes manual)

2. to accomodate for the aftermarket exhaust, what should the pilot screw be set to? leave at the standard 1 5/8 or greater...say 2 or 2 1/4 turns out?

i haven't had a look inside since i bought the bike so i'm just assuming that everything is stock

[Cammo]

1. the bike has been fitted with a TSR can and pipes so which main jet size would you recommend? read somewhere on here that 112 should do from the standard 108 (think that's the standard size according to haynes manual)
Yeah, 112's all around are usually what's recommended on rvf's with a free flowing pipe.

2. to accomodate for the aftermarket exhaust, what should the pilot screw be set to? leave at the standard 1 5/8 or greater...say 2 or 2 1/4 turns out?
Best to leave it at the standard setting (1 & 5/8 turns out) and see how it goes.

[pauliealdridge69]

Alright Cam...i followed your guide but would appreciate a little advice.....i have two bikes...one pulls and revs through 14000 with a standard exhaust, 116 118 jets and hits 130mph, the other bike looks like it is standing still after 60-70 mph.... it had a massive flat spot around 6-7000, ticked over like a dog and topped out at around 100-105 mph. i inherited a full scorpion exhaust (basically straight through) when i bought it. I contacted Rick oliver and he said to put 120/122 jets in cause of this exhaust...i followed your instructions but the bike still tops out at 105 although it pulls much sweeter and ticks over like a dream, if i blip the throttle it tries to die..tooooo rich?? Should i try to lean it down a little? should i use the pilot screw or remove the needle washers to lean it up?? I checked the float heights and they seemed perfect. The other issue i have is if im sat at 105mph and slowly release the throttle it seems to accelerate more, you can feel the bike pull...strange feeling when you're thinking about slowing and cornering lol. Ive got good compression, (same as the other bike) why does it top out early? whats a normal top end?? I definately got the bug...vfr 400's are great...i even removed all the annodised bolts and nuts etc if anyone wants them for their shed collection.

[pauliealdridge69]

i've an '89 and a '92 vfr 400 NC30's...it's the 92 bike im having issues with...there are no intake mods or anything...the battery recently died on me so ive fitted an R6 rectifier and new battery...would this have effected the power out put if the rectifier was pooh and charge was getting worse? Good with the tools not with electrics lol Cheers all...any advice or help is welcome