what effect of raising carb needles?

[Cammo]

Hi, I recently put a new stainless exhaust on my bike and found i had a stuttering spot at 2 1/2 thou revs although the rest of the rev range is ok.

2500 revs is only a bees dick above idle

Main jets and needle shenanigans won't cure this... happy to be proven wrong though!

[stimpy]

flatspot means its lean
you need richer needles
all your doing with raising the needle is moving the fuel to come in sooner...its still going to have the same problem
as the needle is still the same taper....if that makes sense WTF
nc30 needles solved all my probs with 29 carbs.
....theres a tip
stimpy

So why do Mikuni Dynojet & FactoryPro have notches and clips to adjust needle height?

By placing a shim under the needle you raise it to a narrower part of the taper giving you more fuel for a set amount of air i.e. the slide height.



So if the slide is at 3mm lift the shimmed needle is at 3mm + 0.5 (size of shim) = 3.5mm this means you get a richer mixture.

You don't have to remove the carbs to get to the needles.

wazza,why do people buy different needles then?
saying by only moving needles up and down will solve the problem....it doesnt
im sure the taper on a dynojet needle is very different to stock...and you will find that there is also a range of needles in different tapers you can get from these guys.
once you have found the taper that works...then you move it up and down to get the thing to work properly.

firebeast,yep,the nc30 needles are a tad shorter than the nc29s with a different taper...there is an A and a B needle..i used both,but have been told the B needles are the go.espesh with ram air,stock pilot settings,and 155mains
stimpy

[Cammo]

firebeast,yep,the nc30 needles are a tad shorter than the nc29s with a different taper...there is an A and a B needle..i used both,but have been told the B needles are the go.espesh with ram air,stock pilot settings,and 155mains
stimpy

Cool info!

I have a handful of used nc30 B needles if you want em for the price of a postage stamp Scott.

[matt69]

Cool info!

I have a handful of used nc30 B needles if you want em for the price of a postage stamp Scott.

If Stimp doesn't want them I'd be happy to take them off your hands...

Matt

[Waza4]

I've had needles turned down on a lathe to keep the top end fueling so I can lower them too clean up a 2.5K to 3K rich miss fire.This was only after not being able to find a combination of jet, fuel height and needle position that worked.
Because if I dropped the needle it would sort the 2.5K but would not pull so hard above 7K and stopped at 13.5K as apposed to 14K in top, so I uped the jets witch sorted that but the 2.5k problem came back.So by profiling the needle to equate to a notch worth being removed 1/3 rd from the tip.
Happy days.

So the needle can work from 2.5K to the red line.
I'd only change a needle after trying all the other variables first.

But as firebeast said it might be one of those 4 into1 systems where the headers are to short witch might be a real bitch to dial out.

[Davez29]

But as firebeast said it might be one of those 4 into1 systems where the headers are to short witch might be a real bitch to dial out.

Its a 4-2-1 as seen on ebay from Sandybike spares. The only difference I could find is that the manifold pipes are of a bigger diameter and Im supposing that's why things have changed. I do thank everyone for their input as it has brought a good debate on everyone's thought on this matter. as soon as I get time I will start with the pilot scews and go from there ( I still got to find a screwdriver I can get under the carbs with, If I don't take them off).

edit: approx circumference is 11cm as opposed to the original that was around 10cm

dave

[Waza4]

It's only 3mm extra diameter witch does not sound over the top. Ive heard the DK pipes cause trouble.
P.M. your address if you want me to post you some shims.

[firebeast]

i have only ever seen 1 set of needles from dynojet and its not much different than stock,just has some adjuastability to it.it doesnt change anything on the mains if standard,just drilling the slide out and having more responsive springs.
i take it your engine doesnt have a filter to run 155 mains?i have got fully tuned lump set up with a race filter for road use with standard headers and race can and thats only running 124's.its got slotted race cams,ported head,raised comp,3 stage valves124's a lot from 108 standard size.every bike dont run the same as the next,so just try/eliminate 1 thing then move on.
only prob i can see with shorter needles is the lack of adjustment if you wanted to raise it a fair bit.stilll interested to find out tho'.
stickshift,whats the cost of a postage stamp to the uk then?
totally different but related,i have a vfr750 which runs 29 needles as the taper is better and it beefed the midrange lovely!exactly the same length,weird eh!

[stimpy]

this has been a great discussion...quite interesting to hear what people try and had success with
and its true,not everybike runs the same.
stickshift,if you have a set of b needles,i will certainly grab them if thats ok....
do i paypal you the cost of a stamp ?
my email is motascott111@hotmail.com for the finer details
stimpy

[Waza4]

Stimpy are these needles J3WB