NC30 carby jetting - DIY guide

[Drunkn Munky]

I remember now on my 1st RVF i did have 1mm washers and HRC slide springs, that was with 110 jets and stock intake system and a end can. Cheers for clearing that up mark.

So mark, what symtoms would the slide opening to fast give? bogging down?

[CMSMJ1]

I think the slide opening too fast, with the needle too high would give bogging in the midrange.

The lighter spring is, in my opinion, an attempt to give the carb a more flat slide feel where you would pull the slide directly rather than use the vacuum to open it.

I've never ridden these proper carbs...but I have read and cracking the throttle too fast does bog them out.

[Drunkn Munky]

Do we have a diagram anywhere which shows what carb components affect certain parts of the rev range and throttle openings?

Ive seen plenty for 2 strokes but dont recall anything for NC's

[Cammo]

The NC35 hrc slide springs have a lower spring rate than the standard springs so they will be raised more for the same velocity of air, making the mixture richer.

A washer will also raise the needle, but it will raise the needle the same 0.5mm (or whatever sized washer you're using) over the whole of the slide movement. This will have the effect of richening the mid and top range to some extent.

Compared to the standard slide springs, the hrc springs lift the needle a proportionate amount, not a fixed amount like the washer, over the slide range.

So for mine, the hrc slide springs are a smarter option than using extra washers on an NC35.

Here’s a quick diagram to explain (all figures are made up!):



Diagram edited since mark is such a fussy bastard!

[CMSMJ1]

Don't want to be a fussy bastard...but just wanted to clarify a couplf of things in the graph

1: the washer - surely if should start higher than the other 2 traces in the lean/rich scale - seeing as it is already out of the jet a touch before the slide has moved? It should also be parrallel to the std trace??

2: the HRC spring - is it not a linear spring? I was under the impression that it was an all round softer spring.

After putting that down..it would make sense for the HRC spring to be progressive and allow the first 2.3rd of throttle openings whip that slide out further and then ramp up the rate to allow a firmer spring to push the slide back down when off the throttle.

I do like geeky threads..

[Cammo]

Don't want to be a fussy bastard...

Sure Mark!

1: the washer - surely if should start higher than the other 2 traces in the lean/rich scale - seeing as it is already out of the jet a touch before the slide has moved? It should also be parrallel to the std trace??

Yes, you are correct. I'll amend it when I get a quiet moment tomorrow at work

2: the HRC spring - is it not a linear spring? I was under the impression that it was an all round softer spring.

It is a (softer than standard) linear spring, but more force is required the further the spring is compressed. If you think about linear fork springs, you can easily compress them by hand a few cm's, but not much more because the spring force increases. The force required to move them each centimetre increases exponentially the further they're compressed.

The term 'progressive' spring is misleading - all springs are progressive, some just more so than others (such as the standard nc30 fork springs).

I do like geeky threads..

Me too!

[surfer 69-b]

hoi guys
first my nc35 had a smal middrange hole at 6 k
then i fitted a qa throttle an this smal hole became much bigger
next i fitted some washers to raise the needles (and hrc cdi) and it was cured
the only disadventage is i think i have to close the petrol when i leave it standing (if not i can smel petrol but it didn t flood becouse it always started right away if i forgot to close)

from what i understand now the hrc springs would have cured the midrange hole without the washers (and then i wouldn t have to close the petrol of when i leave the bike )

at the moment the bike revs wel through the whole range but if you guy say the springs is the better way to cure the hole i would like to truy this (rest of bike is standard)
groeten michel

[Cammo]

next i fitted some washers to raise the needles (and hrc cdi) and it was cured
the only disadventage is i think i have to close the petrol when i leave it standing (if not i can smel petrol but it didn t flood becouse it always started right away if i forgot to close)

You shouldn't need to turn the fuel tap off just because of these changes. The smell of petrol might be because it's running excessivley rich?

at the moment the bike revs wel through the whole range but if you guy say the springs is the better way to cure the hole i would like to truy this (rest of bike is standard)
groeten michel

I guess the only thing to do is remove the extra washer (1 washer is standard) and see how it goes, or get it dynoed. You can be our guinea pig!

[amaechizzle]

first my nc35 had a smal middrange hole at 6 k

next i fitted some washers to raise the needles (and hrc cdi) and it was cured
groeten michel

I guess the only thing to do is remove the extra washer (1 washer is standard) and see how it goes, or get it dynoed. You can be our guinea pig!

I thought you weren't suppose to put a washer on the nc35's ?

[Cammo]

I thought you weren't suppose to put a washer on the nc35's ?

You could do, but the hrc springs are a better option in my opinion.