Overhauled the NC30 carbs today (results and settings)

[Neosophist]

So today I sorted the carbs on my 30.

The bike has ran great through the revs (except a big flat-spot at 10k) since i've owned it but the idle was around 2000 RPM and erratic.. it'd drift up and down a few hundred RPM's and if you tried to set it any lower than 2000 you'd risk it stalling.

In preparation I brought new carb rubbers.

Today I removed the carbs (came off with a gentle pull) although it was 35c today and the bike was toasty after a long ride so rubbers nice and soft.

Examining the jets found that it was running 110 x 4. The needles were standard J51A / B's in the correct place as were the emulsion tubes.

But everything on the bike is original Honda equipment so expected it to be standard.

Onto the floats then after some liberal cleaning of the float-bowls and emulsion tubes..

I got a piece of cardboard and cut a 6.8mm deep L so I could use it as a float-heigh tool. All of the float-heights were only 3mm!

Adjusted them all up and checked the pilot screws... 1.25 turns out each one! Set these to 2.5 turns out.

Seems somebody may have tried to correct the overly-rich float heigh with the pilot screws.

While the carbs were in pieces Drew (Moriwaki man) kindly went to the local bike shop and got me some new jets, 115 x 2 and 118 x 2.

While he was off I enlarged the vaccum hole to 2.5mm (doesn't seem to have made much difference but have noted it for reference. Going to fit NC24 slides when they arrive, left the 1 shim under the needles.)

Put the 118's in the rear, 115's in the front.

Put the new rubers on and connected up my vaccum gauge.

Put the carbs back on, took about 5 minutes and a little faffing around but no major head-ache.

The bike started first turn of the button after letting the carbs fill with fuel, the idle much better but lumpy.

looked at the balance gauges and they were WAY out, balanced them up (my hand in the V with a 7mm socket!)

Idles rock-solid now, as if somebody has pinned the tacho needle :D have it set just under 1500, so around 1300rpm and it's perfect.

The bike also has no flat-spots and runs great. So the extra washer wasn't needed.

2.5mm hole hasn't caused any problems, maybe it helps with the flat-spot before but changed so much can't isolate it, but noted it.

Can go from idle to limiter without hesitation now though.

Very pleased.

Next week will be overhauling the fron calipers and chaning the brake fluid!

Yamamoto Half System and Endcan btw

[hardnutdvd]

don't you just love it when things go well and there's no major dramas...

[CRM]

good call with the card to set the float heights, i use a plastic business card cut to suit. makes life so easy to check the heights.

[lizard821000]

lucky man, not often it goes that smoothly lol great news mate.

ps, can the airscrews be tweeked with the carbs ON the bike?? iv only set mine to 2 turns out. and there back on now .

[Neosophist]

lucky man, not often it goes that smoothly lol great news mate.

ps, can the airscrews be tweeked with the carbs ON the bike?? iv only set mine to 2 turns out. and there back on now .

Yes, you ideally adjust them when the bike is running

[Neosophist]

good call with the card to set the float heights, i use a plastic business card cut to suit. makes life so easy to check the heights.

Indeed!

I have a float heigh measuring gauge but it's in the UK.

So to recap for anyone working on carbs, i've had great results with

NC30 (1989)

115f / 118 rear
Standard 1 x shim.
2.5 turns pilot screws.
Slide vaccum hole enlarged to 2.5mm.

[Man_Named_Dave]

This is useful, I think I'll switch to these settings this winter. I've always had to run a couple of hundred revs above the recommended 1300 for similar reasons.

[lizard821000]

lucky man, not often it goes that smoothly lol great news mate.

ps, can the airscrews be tweeked with the carbs ON the bike?? iv only set mine to 2 turns out. and there back on now .

Yes, you ideally adjust them when the bike is running

Cheers dude, I rememberd once I had refitted that I set my UK carbs to only the w.s.m setting of 2 turns, thought fk. Was a bitch re-connecting those throttle cables. But iv had a wee look into the float bowl area and see that they can be found lurking there, just about. Will be fun reaching some of them though lol

[porndoguk]

good call with the card to set the float heights, i use a plastic business card cut to suit. makes life so easy to check the heights.

Indeed!

I have a float heigh measuring gauge but it's in the UK.

So to recap for anyone working on carbs, i've had great results with

NC30 (1989)

115f / 118 rear
Standard 1 x shim.
2.5 turns pilot screws.
Slide vaccum hole enlarged to 2.5mm.

this is exactly what im running with Rick O needles, i have to get 24 slides and i got some new pilot jets to drop in as i fucked my old ones after years of abuse it snapped as i tryed removing!

still have a small and i say SMALL flat spot at 5-6k which is less than we previously had at the dyno, im going to see if i can get smaller/thinner shims than the standard 0.5mm gonna be a tough one, i am tempted to run without on the 24 slides?

[Neosophist]

good call with the card to set the float heights, i use a plastic business card cut to suit. makes life so easy to check the heights.

Indeed!

I have a float heigh measuring gauge but it's in the UK.

So to recap for anyone working on carbs, i've had great results with

NC30 (1989)

115f / 118 rear
Standard 1 x shim.
2.5 turns pilot screws.
Slide vaccum hole enlarged to 2.5mm.

this is exactly what im running with Rick O needles, i have to get 24 slides and i got some new pilot jets to drop in as i fucked my old ones after years of abuse it snapped as i tryed removing!

still have a small and i say SMALL flat spot at 5-6k which is less than we previously had at the dyno, im going to see if i can get smaller/thinner shims than the standard 0.5mm gonna be a tough one, i am tempted to run without on the 24 slides?

The NC24 slides are the same as the NC30 ones apart from the rounded bottom and having two holes (2.5mm mimiks this)

They are the same height and the NC24 needles also have one shim.

Your fuelling won't change with the NC24 sliders, you might have a marginal improvement at FULL WOT due to increase in airflow but the slides will raise the same height as the NC30 ones with the 2.5mm mod.

Lowering the needles will make the bike leaner. Have you found out if your flat-spot is being caused by the mixture being lean or rich?

Remove the shims and see if it gets better, if it does it was rich, if it doesn't they need raising.

I'll get some videos taken, mine idles like you've stuck a pin in the tacho, rock solid, super smooth and revs cleanly from idle to red-line in all the gears :D

All of my jets and passageways are super-clean and the carbs balanced and the rubbers new.

It's an odd problem yours. Aftermarket headers or standard system?

I think the Yamamoto half rear does away with some of the flat-spotting, comebined with the 2.5 turns floats..