UK NC carb jetting.....

[speedy231278]

what's wrong ? UK spec jetting is different to jap spec

Yes, but everyone says they run larger rear jets to front stock (ie 120/122), yet the diagram shows 122/120 front to rear...

[porndoguk]

running different sized jets was found to be pointless by kev at projex, he did A/F tests on individual pipes in which he fitted (perminantly) sensors, he found them to be identical between the front and rears they say the rears run hotter but they dont its a case of the the front runs cooler from the ambient airflow,

i run 125s all round and pulls really well tbh.

[Cammo]

what's wrong ? UK spec jetting is different to jap spec

Yes, but everyone says they run larger rear jets to front stock (ie 120/122), yet the diagram shows 122/120 front to rear...

I think my advice on uk standard jets is wrong in the guide, apologies for the confusion!

[arsey30]

The Honda workshop manual shows mains 122F 120R.
The F/R needles and R jet holder are all obsolete, but the F jet holder [emulsion tube] is still available.

I have ordered one, so that way we will be sure which jet holders go where.
Unsure about needles, but am inclined go richer to front as per main jets.

[pip]

The Honda workshop manual shows mains 122F 120R.
The F/R needles and R jet holder are all obsolete, but the F jet holder [emulsion tube] is still available.

I have ordered one, so that way we will be sure which jet holders go where.
Unsure about needles, but am inclined go richer to front as per main jets.

Great stuff, this was confirmed by Paul CRM, earlier when I pm'd him.

Do you know if there is a shim/washer under the needle, it's bad to tell from the online fiche - I never put one in, for right or wrong.

Folks have been pi$$ing about with these carbs for 20 odd years, I can't believe there isn't a bullet point resource for basic standard carb setup for various build models on these bikes

Thanks for the input guy's, I feel like I'm getting there!

Only 3 valves were out & only by a smidgen, all the others were +/- .02mm of the upper clearance. Just waiting for shims to arrive.
Next, sorting the 2 snapped exhaust studs.......
Otherwise all looks good, even the lower radiator is one of the best I have seen

Phil

[speedy231278]

what's wrong ? UK spec jetting is different to jap spec

Yes, but everyone says they run larger rear jets to front stock (ie 120/122), yet the diagram shows 122/120 front to rear...

I think my advice on uk standard jets is wrong in the guide, apologies for the confusion!

Still doesn't explain countless other sources other than this forum where people with staggered jet sizes have the fatter ones at the back!

[Cammo]

No it doesn't, personally I wouldn't run larger jets at the front, regardless of what uk Honda says.

The uk needles use a single washer under them the same as all other models.

[Neosophist]

I have to goto work soon and I'm very sleepy so this will be quick for now. Firstly I don't think its logical to write off staggered jetting completely based on a couple of dyno runs on one bike that didn't run very well in the first place, maybe for that particular bike then yes.

Based on their success with motorcycles I will assume they know how to set the bike up correctly for their intended purpose.

Now, onto the question of why.

Only conjecture but the rear cylinders usually run warmer (people often cite this as air-flow and they are at the back but its a water cooled engine) the real reason is the oil and water passes through the front bank first, so its warmer by the time it reaches the rear blocks.

The NC30 UK model has an oil cooler too, so as the oil is slightly cooler than stock I assume, then perhaps the front bank can generate slightly more power without overheating the bike too drastically.

Only conjecture.

Most people are running non-stock systems and things anyway so as Ricks bike is a classic example, best to get it set-up ideally a at a dyno-shop.

For his bike equal jetting all around gave the best performance (is it still equal?) so depending on many factors even engine condition stock may no longer be the way to go.

UK Emulsion tubes are different to JDM ones too but the more holes go in the rear

[pip]

Cheers guy's all good info.

I'm quite happy that the big H have a bit of an idea on how to make a bike run well & reliably, hence going for completely stock.
I'll get a dyno run & fine tune from there.

Having said that, they have pee'd about with jetting - same, bigger front, bigger rear, diffrent needles etc on various of their V engines over the years!

Any indication for the correct location for the A/B needles before I remove the slides again to fit the washer.....

Pip

[arsey30]

The workshop manual shows 1 shim under the needle, but no indication if 0.5mm or 1.0mm [typical values]

Out of interest, I note that the RC30 main jets [similar V4 motor] are the same way round [richer fronts] as UK NC30, for the UK and rest of the world production, but I don't know about Japan.
The needles and emulsion tubes are the same front/rear.