what effect of raising carb needles?

[Davez29]

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. Well I asked about it and someone said just raise the carb needles. So as I have my bike in bits re-painting it I thought I would look into this possible fix.

Now what I really need to know is how far I should raise the needles and what should I expect to happen to the rest of the range, which is ok at the moment it seems, its just at 2 1/2 I have a problem. Any help in this would be appreciated as I really don't know anything about carbs, although I did successfully take them apart and clean them several months ago, without problem.


dave

[Cammo]

Forget raising the needles, your pilot screw settings will be responsible for this.

Try richening them 1/4 turn.

It depends what bike you have as to which way the screws turn for this.

[Davez29]

It depends what bike you have as to which way the screws turn for this.

Hi and thank you for the info, I have a later model NC29, if you could enlighten me which way to turn the pilot screws it would also be helpful.

cheers

dave

[Waza4]

I think its out for more fuel it is on the early 29. I think the backward thing is on the RVF witch sort of sums up V4's

2.5K is really the float chamber territory but its a real ass with plastic floats if the pilot settings don't work (but it should work ) I,ll stick some shims in the in the post for you.

[brooky]

i had the same problem on my 23 a few years ago, increased the jet size by 1 size and it cured the problem

[Davez29]

Ok and thanks for the help, was thinking it might be screw out for the correction but got confused with Stickshifts answer. It also seems that LozVTRs latest thread is connected to my shenanigans so will be gleaning info from this also.

I will keep you informed of developments as soon as I can get back on the road to test these answers out.

Dave

[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
nc30 needles solved all my probs with 29 carbs.
....theres a tip
stimpy

[Davez29]

Ok thanks stimpy, something else to consider if the pilot screw method dont work.

One thing, just got home from work and took a quick look at the haynes manual, it looks like the pilot screws are under the carbs in a hard to reach place, so to me looks like its going to carbs off to reset the screws, if so it looks like I cant set them using the method in the other thread, so will be hit and miss with maybe a lot of carbs off and on until its correct, damn. Is this correct?

[Waza4]

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.

[firebeast]

is the new exhaust the same 4-2-1 replica or is it the dodgy 4-1?have heard bad reports about smooth power on those so moving the needle may create new probs further up,but you wont know without trying.waza'a right so would recommend doing the pilots first.didnt realise 30 needles go in.interesting to find out if they are similar to dynojet needles.anyone got a spare set i can borrow for a while?
also get the engine warm before you take the carbs off and they will pop on and off a lot easier.you can get carbs off in ten minutes if you prop up the tank,you just need to male sure you have got a very long philips screwdriver before starting.dont need to take any cables off etc to adjust pilots.or right angle screwdriver and small mirror might do the job!