HRC carb setup - NC30

[Jamboy]

Didn't Rick Oliver look into having these made afew years back?

[kevprojex]

I coulnd find hrc stacks anyware when i tuned my old nc30 but i modded the original nc30 stacks ,heres what i did with mine, i warmed the stock rubber inlet stacks up with a heat gun to make them soft ,then i folded the rubber stack over itself on the outside making the stack shorter by about 20 or 25mm shorter cant remember exact now its a few years ago, this also gives the inlet edge a bigger radius which can only be good for air flow ,its a bit tricky to do as they keep springing back up to start with , i did them one at a time keeping them warm with the gun, once i had the rubber folded over i just put a steel ring around the rubber untill it cooled down , once cooled it stayed there but for added piece of mind a glued them down permently so they didnt spring back up into shape.And before any anoracks jump in and start pulling the post to bits I KNOW its not a HRC stack but its a lot shorter than the stock inlet rubbers with a smoother radius into the stack and its FREE.

[CMSMJ1]

The main issue I found with trying to run this setup was the lack of the shroud that the proper HRC stacks have.

I gave up..couldn't be arsed for what I was using my bike for.

[lukemillar]

Ok, I know the long answer (head to my nearest dyno!) However, I am racing tomorrow and could do with and quick advice anyone would like to offer!

Just got back from a practice day running the HRC carb setup and have a few things to note:

Good stuff:
1- The sound is incredible!
2- The power I get from 8/9k and up is awesome

Not so good stuff:
1- I get a lot of stumbling from 4k-7k. In neutral on stands, it revs freely to the redline and back. However, so soon as I hit the track, if I let the revs drop too far mid corner and start to roll on, I get a stumble and then a sudden kick of power at 7k+

The setup is:

145 Mains front
147.5 Mains Rear
Rick O's emulsion tubes and pilot jets #40
8ZF needles with 0.5 mm washer
HRC slides
2mm hole in the air jets (faking the HRC velocity stack shroud)
Pilot screws (2 turns out. I started with 1.5, but got an idle all over the place. 2 turns seems better)
short velocity stacks, drilled carb bracket and fibreglass HRC replica tray.

So, I have one evening to ponder and then tomorrow morning after qualifying to make changes! If anyone has any insight or ideas, then that would be great!

Thanks
Luke

[Jamboy]

My brother is running this set up with genuine HRC carbs , his is running 145 mains alround and no 0.5 washer as he said it ran better with out.
He is also running a full ethos exhaust and is running the HRC map in the cdi.
His seems to be fine at that and produced a strong 65hp on the dyno.
His top end speed over mine is far better because he can past me on the long straights with ease.

[reverse cylinder jim]

Ok, I know the long answer (head to my nearest dyno!) However, I am racing tomorrow and could do with and quick advice anyone would like to offer!

Just got back from a practice day running the HRC carb setup and have a few things to note:

Good stuff:
1- The sound is incredible!
2- The power I get from 8/9k and up is awesome

Not so good stuff:
1- I get a lot of stumbling from 4k-7k. In neutral on stands, it revs freely to the redline and back. However, so soon as I hit the track, if I let the revs drop too far mid corner and start to roll on, I get a stumble and then a sudden kick of power at 7k+

The setup is:

145 Mains front
147.5 Mains Rear
Rick O's emulsion tubes and pilot jets #40
8ZF needles with 0.5 mm washer
HRC slides
2mm hole in the air jets (faking the HRC velocity stack shroud)
Pilot screws (2 turns out. I started with 1.5, but got an idle all over the place. 2 turns seems better)
short velocity stacks, drilled carb bracket and fibreglass HRC replica tray.

So, I have one evening to ponder and then tomorrow morning after qualifying to make changes! If anyone has any insight or ideas, then that would be great!

Thanks
Luke

Its just taken about three hours of dyno work this morning to get rid of the flatspot between 5 and 7 on my bike running the hrc carbs that you have described.
Ive gone from 45 mains to 34's, 40 pilots to 35's and now running nc24 needles. Your jetting was the same as mine but was far far too rich for my bike. Is your bike engine highly tuned? full system?

[lukemillar]

Thanks for the quick reply guys! When I got to the track and out in qualifying, the bike was pretty good! As long as I kept it above 8k then I didn't have any real issues so I kept it as is. However, the stumbling really caused my race starts to suck. Still, now I have more time, I can start playing.

I managed to solve the main issue which was incorrect float height - 2 were too high and 2 were too low. I think 2 of the carbs were flooding which is causing the bogging and cutting out.