NC30 carby jetting - DIY guide

Forum rules
Please can you post items for sale or wanted in the correct For Sale section. Items / bikes for sale here will be removed without warning. Reasons for this are in the FAQ. Thanks
User avatar
Cammo
Site Supporter
Site Supporter
Reactions:
Posts: 5525
Joined: Thu May 01, 2008 12:35 am
Bike owned: NC30
Location: Melbourne, Australia
Re: NC30 carby jetting - DIY guide

Post by Cammo » Tue Jan 21, 2014 11:28 pm

NC30Dubz wrote:Ok. It could be fuel starvation aswell thinking about it, but I wouldn't understand why? Yes, it was on the road, took it for a run after fitting the jets and washers, was fine on a low speed run but as soon as I went full twist, the bike didn't like it
Did you put the fuel vacuum line back on the tap? Fuel tap to 'On', etc?

Check that each vacuum slide is springing back properly after you raise them up with your fingers. If the slide covers are not on properly the slides won't work.

Those size jets will be fine, even if they were slightly too large (not likely) it won't cause the symptoms you describe.
"It's just a ride" Bill Hicks

NC30Dubz
Settled in member
Reactions:
Posts: 75
Joined: Wed Feb 23, 2011 11:22 pm
Bike owned: VFR400R NC30 (Polly)
Location: Hemel Hempstead, Hertfordshire
Re: NC30 carby jetting - DIY guide

Post by NC30Dubz » Wed Jan 22, 2014 9:26 am

Thanks,

The vacuum hose is on, and as for the slides, I do teat the carbs before I put them back on and one of them did stick but released itself after a few minutes, is there a way I can grease these up so they move more freely?

NC30Dubz
Settled in member
Reactions:
Posts: 75
Joined: Wed Feb 23, 2011 11:22 pm
Bike owned: VFR400R NC30 (Polly)
Location: Hemel Hempstead, Hertfordshire
Re: NC30 carby jetting - DIY guide

Post by NC30Dubz » Wed Jan 22, 2014 1:54 pm

Just taken it apart again, the slides are moving, I checked the pilot screws , moved them to 2.25 turns, and it's still bogging down in the high rpm, could it be that I should set the screws to 2 turns? Just a thought, the main jets I'm using (120's) are off an old set of carbs I had and look a bit.. used, could it be that be used they're old and used that they could be hindering the flow of fuel? I'm in the process of ordering a new set of 118's and 120's as I've been told that they are the best set up to use.. any help is appreciated! Thanks.

mrpaintdude
Settled in member
Reactions:
Posts: 11
Joined: Sat Jul 24, 2010 4:40 pm
Bike owned: NC30
Location: Bishops Stortford
Re: NC30 carby jetting - DIY guide

Post by mrpaintdude » Fri Feb 28, 2014 11:14 pm

That looks like a proper thorough step by step guide. I'm having major flat spot issues on my NC30, any chance you can send me a PDF copy?

User avatar
Cammo
Site Supporter
Site Supporter
Reactions:
Posts: 5525
Joined: Thu May 01, 2008 12:35 am
Bike owned: NC30
Location: Melbourne, Australia
Re: NC30 carby jetting - DIY guide

Post by Cammo » Sat Mar 01, 2014 3:40 am

mrpaintdude wrote: I'm having major flat spot issues on my NC30, any chance you can send me a PDF copy?
PM sent with a link to the document library: http://www.400greybike.com/docs.htm
"It's just a ride" Bill Hicks

britaxcooper
Settled in member
Reactions:
Posts: 133
Joined: Sat Oct 11, 2008 11:46 pm
Bike owned: NC30
Re: NC30 carby jetting - DIY guide

Post by britaxcooper » Sun Mar 02, 2014 10:05 pm

NC30Dubz wrote:I've got a yamamoto half system with a stubby exhaust, yes its a standard intake minus a bit of the plastic, there is 1 washer as standard on all the needles, added an extra 0.5mm washer to each at the same time as the jets.
I've just fitted a Yamamoto system with a very free flowing silencer.

Just checked the mains and theyre 120 all round.

I've not ran the bike yet, but I'm guessing I will need to change the mains? Would I be advised to fit 122's in the rear carbs and leave the fronts at 120?
I'm going to do the other mods on the first page of this thread at the same time.

User avatar
Cammo
Site Supporter
Site Supporter
Reactions:
Posts: 5525
Joined: Thu May 01, 2008 12:35 am
Bike owned: NC30
Location: Melbourne, Australia
Re: NC30 carby jetting - DIY guide

Post by Cammo » Mon Mar 03, 2014 8:30 pm

I would just leave them at 120 all round, should be well suited to your setup.
"It's just a ride" Bill Hicks

User avatar
GeeTee
NWAA Supporter
NWAA Supporter
Reactions:
Posts: 282
Joined: Mon Jan 20, 2014 1:27 am
Bike owned: NC30 & GSXR750K4
Location: Dartford, Kent, United Kingdom
Re: NC30 carby jetting - DIY guide

Post by GeeTee » Mon Apr 14, 2014 11:20 am

Damn.. after re-reading the DIY guide I just spotted the 0.5mm needle washers, and my needles have no washer fitted at the moment. My carbs were in an awful state of tune (the whole bike was), and I stripped, cleaned and rebuilt them a few weeks back. It had 125 mains all round and pilot screws were all over the place, set between 1.5 and 3 turns out with no two the same. I've drilled the slides, gone back to 118/120 mains and reset pilots to 2.25 turns out. The engine is stock NC30 with a Delkavic carbon can + K&N filter. Seems to start really well now and tickover is nice and steady. It has a very slight flat spot just off idle when I snap the throttle. I'm wondering if the lack of needle washer could be the culprit, but can't be arsed to strip it again to fix it. I've a trackday booked at brands on the 30th April, and considering running it as is and fine tune it afterwards.. maybe on a Dyno. I've got loads of new stuff fitted to bed in (tyres,brake pads, new discs all round, suspension upgrades to dial in etc..) so won't be pushing it anyway.

User avatar
Cammo
Site Supporter
Site Supporter
Reactions:
Posts: 5525
Joined: Thu May 01, 2008 12:35 am
Bike owned: NC30
Location: Melbourne, Australia
Re: NC30 carby jetting - DIY guide

Post by Cammo » Tue Apr 15, 2014 12:50 am

GeeTee wrote:Damn.. after re-reading the DIY guide I just spotted the 0.5mm needle washers, and my needles have no washer fitted at the moment.

I've got loads of new stuff fitted to bed in ... so won't be pushing it anyway.
I wouldn't worry too much, the lack of washer won't affect the high rpm fuelling at all, though you might find it will affect the rideability (lean) in the fuelling transition from needle to main jet (around 7-10,000 rpm).

Might be an idea to pack the washers and take some tools with you to the track!
"It's just a ride" Bill Hicks

User avatar
GeeTee
NWAA Supporter
NWAA Supporter
Reactions:
Posts: 282
Joined: Mon Jan 20, 2014 1:27 am
Bike owned: NC30 & GSXR750K4
Location: Dartford, Kent, United Kingdom
Re: NC30 carby jetting - DIY guide

Post by GeeTee » Tue Apr 15, 2014 1:44 pm

I'll try to ride it as is on the day and tackle it when I get home. I could easily spend half the session in the garage if I decide to pull carbs off. The rear cylinder slide covers are pretty accessable on the bike, but the front ones are well hidden. I'm wonderng if the bigger 125 mains were masking the fact that the washers were missing. I was running the bike on a small 1/2 litre tank suspended from garage roof. So it could be a fuel starvation issue due to lack of fuel flow.


Post Reply

Return to “V4 - Workshop”