NC30 HRC open carb setup

[hunter]

Had a look today,
main jet front 145
rear 120.
pilots 35
emulsion tubes front and rear 8 hole.
Spring slightly shorter tighter coils and softer than std.
No idetification on needles but have six grooves,
I will get a pic next time.

Pic sorry it's so crap.
The 24mm measurement should have read 25mm.

[lukemillar]

I just remove them completely and leave the spigots as is like in Hunter's pic

[skinnydog0_0]

Hi All,

Got my bike running today and its revving at 7k tickover

I dont think i have an air leak on the rubbers, i have a feeling its the pilot screw setting.
I have put mine to 2 1/4 turns out
Standard is 2 turns.

Jets are
135 rear
140 front
Pilot jet 40
G needles
0.5 shim

HRC carb slides with rounded bottom


does anyone with this setup remember what they set theirs too?
If its not this then i think the butterflies must be open to much. I havent balanced the carbs, but after getting them back together i use a feeler guage to set the butterfly gaps to 0.15mm so it will run.
Perhaps this gap is too big?

Any thoughts?

Cheers

[CMSMJ1]

chokes open?

[skinnydog0_0]

Hi Mark,
No i think i have sussed the issue. I was running the pilot screws at 2 1/2 turns and the HRC manual recons 1 1/2.
Also with the HRC slides i was getting more airflow than before so tis would have made it even worse.
I'll run the bike again tomorrow once i get the carbs back on and see how it goes.
Also do you/peeps reckon the jets are on the lean side for open carbs, as i have read most people run 145's +???

[28hodge]

Yes, I had mine at dynopro couple weeks back with 145 and 147.5 mains and it was lean, I reckon you want to get some bigger jets in

[skinnydog0_0]

Yes, I had mine at dynopro couple weeks back with 145 and 147.5 mains and it was lean, I reckon you want to get some bigger jets in

yes thats kinda what i thought.
Do you remember what size jets you went up to kurt?
I'll probably start at 150 155

[28hodge]

In truth we did away with the open setup, chris dyno'd it and it gave good power at 62.9 the he left all the cards as they were dropped the mains to 136's put the stock filter and airbox on dyno'd it again and got the exact same result. Then he played to smooth it up.

He's not a fan of the open carbs as they obviously allow muck in and this Pitts the valves and kills rings etc.

I'd imagine 150's but every engine is different and mines always seemed to need big jets in, it's had the heads ported so whether this helps the airflow a lot requiring big jets I'm not sure!

[reverse cylinder jim]

Hi here are the settings I had on my old track dog when running open carbs.
Mains, 132fr 134rr
Pilot jet, 35
Hrc immulsion tubes
Air screw 1.5 turns out
I was running nc24 needles and slides

James

[Tim400GB]

My open top carbs run quite well (not dyno'd yet though) on:
Rick Oliver HRC needles
#40PJs
#142.5MJ F+R
RO emulsion tubes
Nc24 slides
Mixture screw set to 1.5 turns out.