Modding the V/stacks on the NC30

[skinnydog0_0]

A sharp exacto knife will do the job.

To start with, you want to cut the stack just above the bottom rib leaving a few mm of rubber above it. Then shave material off above the rib gradually as you're working your way around - until you get level with the top of the rib (this will be the top surface of the cut-down stack and allows you to put a nice internal curve on it). Then do the same on the inside until you get a nice curve. The trick is to take very small amounts of rubber off with each shave. You tend to loose a little bit of rubber where the airjet sits as it is very thin there when cut down.

Then sand with 400 grit (ish) wet and dry (dry) and finish with 1200 grit wet for a nice smooth and shiny finish. In the end, it doesn't have to be perfect, but smooth is good.

The pic below should give you a better idea - you can see how the rib allows you to make a nice internal curve.



Could have sent you a set a couple of weeks ago, but looks like I've binned 3 of them. Go figure

Thanks Superlite, that looks like a very neat and tidy job. Always the way with the ones you binned, you never think that they will be needed till the day after
I have a feeling that my fingers will end up shredded after dealing with sharp knives and flexible rubber

[Cammo]

I was mixed up, there is no base jetting setup in the NC30 hrc manual (only for RVF400).

But you can tell what a typical jetting setup might be from the parts that are offered (the following is taken from the SS/SP manual which is realistically closer to most engine specs than the true F3 spec):

35 - 40 pilot jets
140 - 150 main jets
8zf/8zg needles and 0.5mm or 1.0mm washer
Pilot screws 1.5 turns out


I use 40 pilot jets, and 140 mains (I also change this between Winter & Summer setups, but let's leave that alone for now...). Fuel flows through the pilot circuit at all load levels, so if for example you used 35 pilot jets (standard size) you would need to up the jet size to compensate (e.g. 145's) to achive the same overall fuelling effect as 40/140's.

I find that using the larger 40 pilot jets the extra fuelling at all revs can help alleviate any minor midrange issues when the fuelling is in transition from the needle to the main jet. Believe me, it works!

Finding the correct combination of HRC needles and washer height are less of a concern and are at any rate not critical to the safe fuelling of the engine as fuelling at WOT is. Sorting needle type and height should be last priority.

After you decide on a pilot jet size to use, the correct main jet size for your setup is entirely dependent on the size that you've restricted your air jets to. I can't recommend a size because I use the hrc stacks. I've yet to come across data that can reliably tell you what main jet size to use for a ##mm air jet restriction. Perhaps you can tell us!

What I would recommend though is that you use the biggest pilot jets possible and then tune the main jets on a dyno (or a wideband air/fuel logger), erring on the size of bigger mains (e.g. 150) and working down.

Hope that helps.

[skinnydog0_0]

Thanks Cammo, that is very very useful info, and a great place to start. Once i have the carbs built and on the bike, i will get it on the dyno, and take notes of all the changes (air restrictor/main jet sizes) and post the outcome. I'll make sure i have a pocket full of different jets to make sure all bases are covered

[Cammo]

Sounds good mate.


3 examples of main jet sizes required based on air jet size restriction for a full open carbs style setup:

- For a fully blocked air jet (e.g. no hole drilled and no air getting through) you would be needing something in the region of 132 main jets as a starter. I wouldn't recommend fully blocking them as the air helps emulsify the fuel with air, but many people commonly block them totally up when running ram air. This is an option however.

- For the hrc stacks (unknown size restriction due to the shape of the v-stack shroud), a good starting point would be 145 main jets

- If you don't restrict the air jets in any way (not recommended, you'll end up with a massive midrange revs hole!), you would need to use something in the region of 155 sized main jets.

All of the above is based on using 40 sized pilot jets, as these contribute to fuel flow throughout the rev range), the main jet size needs to be bigger if you use smaller pilots.

From this you can work out a good starting point.

[skinnydog0_0]

Sounds good mate.


3 examples of main jet sizes required based on air jet size restriction for a full open carbs style setup:

- For a fully blocked air jet (e.g. no hole drilled and no air getting through) you would be needing something in the region of 132 main jets as a starter. I wouldn't recommend fully blocking them as the air helps emulsify the fuel with air, but many people commonly block them totally up when running ram air. This is an option however.

- For the hrc stacks (unknown size restriction due to the shape of the v-stack shroud), a good starting point would be 145 main jets

- If you don't restrict the air jets in any way (not recommended, you'll end up with a massive midrange revs hole!), you would need to use something in the region of 155 sized main jets.

All of the above is based on using 40 sized pilot jets, as these contribute to fuel flow throughout the rev range), the main jet size needs to be bigger if you use smaller pilots.

From this you can work out a good starting point.

Thanks Cammo, I will make sure i take those sizes, and as many others as i can get my hands on.