NC21 & NC24 Carbs.(Tuning/information) - please sticky this

[Neosophist]

Since there seems to be a lot of confusion about what carbs / jets go on what bike I thought i'd finally spend 30 minutes with my service manuals and parts books and write it up.

That way you'll know if your carbs are original, been messed with / replaced.

First, look up your model and see what type of carbs they came with VDxxx... After this 5 digit model number there is another letter in brackets, this is the revision of the carbs.

NC21 Models

VFR400Z (VFR400ZG)
VFR400R (VFR400RG)
VFR400R (VFR400RG-YA)

All of these models came with VDA0A carburettors

VFR400Z (VFR400ZH)

This model came with VDE2A carburettors

NC24 Models

All of these models came with VDE2C carburettors.

Carburettor Revisions

If you have read above, you should know which model of carbs came fitted to your bike, now if you read below you'll be able to determine which revision of the carbs were on the bike and what the specs of them are/

VDA0A

VDA0A carbs (For the NC21 bikes listed above) come in two revisions, (A) and (B)

VDA0A (A) revision carbs were fitted on bikes upto frame number 1037018
VDA0A (B) revision carbs were fitted on bikes from frame number 1037019

All VDA0A carbs have 110 Main jets in the Rear carbs and 112 Main jets in the front carbs.

The also have the same emulsion tubes all around. (I can't remember if there 4 or 5 hole, I'm thinking 5 hole)

These carbs do NOT have rubber velocity stacks attached to them, instead they just have a carb plate.


VDE2A

VDE2A carbs (There are only fitted on the NC21 VFR400ZH) and come in four revisions, (A), (B), (C) and (D)

VDE2A (A) revision carbs were fitted on bikes from frame number 1053726
VDE2A (B) revision carbs were fitted on bikes between frame numbers 1053727 to 1062852
VDE2A (C) revision carbs were fitted on bikes between frame numbers 1062853 to 1065212
VDE2A (D) revision carbs were fitted on bikes from frame number 1065213

These carbs have different part numbers listed for their emulsion tubes from the VDA0A carbs.

The rear emulsion tubes are the same on all 4 revisions of these carbs. However, the Front emulsion tubes are different on the (A) revision. The (B),(C),(D) revision all have the same front emulsion tubes, but they are a different part number to the (A) revision.

All 4 revision of the VDE2A carbs are fitted with 115 jets in the Rear cylinders and 112 jets in the front cylinders.

These were the first carbs that came with the rubber velocity stacks fitted (which is where the confusion about NC21 carbs having stacks / not having stacks came from)

VDE2C

These carbs were fitted to the NC24 models, they were available in 5 revisions. (A),(B),(D),(E),(F). No idea where there wasn't a C model.

But anyhow.

VDE2C (A) revision carbs were fitted on bikes from frame number 1051186
VDE2C (B) revision carbs were fitted on bikes between frame numbers 1051187 to 1053088
VDE2C (D) revision carbs were fitted on bikes between frame numbers 1053089 to 1060145
VDE2C (E) revision carbs were fitted on bikes between frame numbers 1060146 to 1065212
VDE2C (F) revision carbs were fitted on bikes after frame number 1070015

The (E) revision carbs were also fitted to RJ-3 bikes upto frame number 1070014
The (F) revision carbs were also fitted to RH-2 bikes from frame number 1065213

The (E) / (F) crossover is probably due to old stock.

All revisions of these carbs have rubber velocity stacks.

All revisions of these carbs have 115 jets in the REAR cylinders.

(A) and (B) revisions have 112 jets in the FRONT cylinders.

All later revisions (D),(E),(F) have 115 jets in the FRONT cylinders.

All of these bikes have the same emulsion tubes... matching front and matching rear.. the ones with more holes go in the rear.

Sliders

Some models of these carburettors come with the rounded bottom sliders that are more favourable to tuners as they provide greater air-flow and they have improved throttle response.

There are 4 revisions of the sliders fitted in these various carbs. I'm not sure which ones are the rounded sliders. Although i'd guess it'd be the later ones.

VDA0A (NC21)

The VDA0A carbs all have the same sliders, these are flat-bottomed.

VDE2A (NC21)

The (A) revision carbs have the same sliders as the (A) and (B) revision NC24 carbs. (early NC24 carbs)

I suspect these are flat bottomed.

The (B) and (C) revision carbs have the same sliders as the (D) and (E) revision NC24 carbs. (mid NC24 carbs)

I suspect these are curved bottomed.

the (D) revision carbs have the same sliders as the (F) revision NC24 carbs (latest NC24 carbs)

I suspect these are curved bottomed.

VDE2C (NC24)

The (A) and (B) revision carbs share the same slider as the (A) revision NC21 VDE2A carbs.

I suspect these are flat-bottomed.

The (D) and (E) revision carbs have a later part number and share sliders as the (B) and (C) revision carbs of the NC21 VDE2A.

I suspect these are curved bottomed.

The (F) revision carbs share the same slider as the (D) revision VDE2A NC21 carbs.

I suspect these are curved bottomed.

Slider Springs

Another interesting factoid about the actual springs in the sliders.

The VDA0A carbs all have the same slide springs.

The NC21 ZH (VDE2A) carbs upto revision (B) and the NC24 carbs (VDE2C) upto revision (D) have a revised carb spring.

The NC21 ZH (VDE2A) carbs from revision (C) and the NC24 carbs (VDE2C) from revision (E) have yet another revised carb spring.. this one has (V.P) in brackets after the name.. does anyone know what this means?

Tuning

I believe the VDA0A carbs are 30mm bore, so changing the rubbers and upgrading to later carbs would help if your after better fueling, especially with an after-market can as the standard carbs on the 21's were quite lean.

The later carbs are 32mm too, so the increased air-flow will help.

The Rounded slider carbs have 2 air-holes for improved throttle respsone, so you do not need to drill them out!

Standard flat bottom slides with one hole can be drilled out.

So there you have it folks. As you can see.. the early NC21s had quite simpler carbs, but the NC21 ZH, the second of the semi-naked 21's (this would be the NC21 to go for) is very much like the NC24.. even having a late production run and having NC24 style carbs with Round sliders and velocity stacks, as well as updated jetting.

If you have a naked 21 and not sure if it is a ZG or a ZH, the ZH was black and red, the ZG was white and red.

Hope this helps people, if theres any suggestions or more info you want to request / add please feel free.

Pictures of each revision of Emulsion tube would be awesome (i'm trying to do something like this with the millions of revisions of ZXR carbs).. unforturantly you can't get most of them new anymore so ordering fresh ones to 'see' what they look like it out of the question. The only differences are going to be holes and spacing, but it is still interesting to see how they changed and have it documented.

Well.. that should clear up things a bit.

[Chrissy_J]

Well, that all looks pretty comprehensive.

Thanks for doing the book-work for us!