NC30 carby jetting - DIY guide

[mattjc]

in this bit 'test the slides to see that the diaphragm is seated properly by pushing each slide up in the carb' where exactly or what am I pushing, sorry to be a pain but this is the only section where I get a little lost and I want to make sure I understand everything before I start.

Also if my bike runs a full system to which i'll be matching the jets to would you place the .5mm washers in, or see how it runs first? My logic is change em while the they're apart...

[superlite]

in this bit 'test the slides to see that the diaphragm is seated properly by pushing each slide up in the carb' where exactly or what am I pushing, sorry to be a pain but this is the only section where I get a little lost and I want to make sure I understand everything before I start.

Basically you stick your finger down the bore of a carb (from the top) and push the slide (the black plastic thing that holds the needle) horizontally back into the carb body, then let go - repeat for each carb. If all the slides return nicely under their own force (keeping in mind that the vacuum will stop them from 'springing' back quickly), they're all good. There's often a slight difference in return speeds between each carb - you're only in trouble if a slide sticks or fails to return really. Saves you some pain if you refit the carbs and find that the diaphragms aren't seated properly

Also if my bike runs a full system to which i'll be matching the jets to would you place the .5mm washers in, or see how it runs first? My logic is change em while the they're apart...

The extra washer works on some NC30s and not on others. Two trains of thought here: try it as is and see how it goes, or chuck the extra washer in and see how it goes - either option could require the carbs off again if it doesn't work, so just have a crack either way I reckon

[born2ride]

good write up there dude, found it when serching for some new diaphagms. just been given an nc30 thats been sat 4 13 years and been giving her a total overhaul. the petrol in the carbs was like resin!

reason i was looking for new diaphrams is because the sliders tend to slide back well most of the way and intermittantly pop back near the end of their travel. swaping the diaphram/slider between carbs transferes the problem. do you think that soaking them in petrol should cure this or is there a better way to soften the rubber up? the rubber seems quite stiff and a smear of silicone grease did help slightly. Are there any other reasons this could happen? im certain theres no air leaks. Cheers for any advice

[Cammo]

Yeah it sounds like the rubber has contracted. If you leave them dry for too long they will never seat properly.

Try soaking them in petrol overnight before spending on another set, it loosens the rubber up nicely.

[born2ride]

cheers will do, better than 35 quid per diaphagm, was just a bit concerned the rubber would react and swell being left in petrol. worth a try tho. thanx 4 the advise

[mattjc]

Just completed your guide today, but need your help! Lol, as it now runs like a sack of your finest...

Full aftermarket Tyga system, replaced the jets to the recommended sizes from RO, also added the washers to the needles, and emptied a can of carb cleaner and set the screws to 2.25 turns out. No problems following the guide only putting the carbs back on - not a nice job my hands will never feel the same again, so with the confidence gained that all was well I started the bike and it worked, twist the throttle and bang out shoot some flames? It hunts through out the rev range and the rev counter looks very erratic - HELP please.

Got to go back in but not without new carbs rubbers (already ordered!), so what do I look out for. Could the extra washer make the bike this rich, or could it be lack of air?

[Cammo]

Flames = too much air!

PM sent.

[mattjc]

Thanks Cammo for all your support, new rubbers, plugs (a serious lack of skin on my knuckles due to the top radiator), and checked everything over again, after a long while managed to get the bike started as it was possibly flooded?

It doesn't seem right at all at the mo, has developed a flat spot at around 10.000, so I think removing the extra washer will help?

It's also a bit "growly" and the revs hang when you let off the throttle, and seems a bit "fluffy" when revving - please excuse the "...." hope it makes some sense, it's just not quite there yet, No Flames this time though!

Thanks again

Matt

[pauliealdridge69]

Worked spot on for me....mate had to stand on the carb's while i did them up but runs like a dream
Drilled with 120/122.5 with 1mm washers and the 2.5mm holes opened up....have gone mad and done the oil..filter...plugs...blead and changed the brake fluid too....any tips for adjusting/lubricating the yokes and forks etc would be much appreciated
Many thanks Paul

[Cammo]

It doesn't seem right at all at the mo, has developed a flat spot at around 10.000, so I think removing the extra washer will help?

It's also a bit "growly" and the revs hang when you let off the throttle, and seems a bit "fluffy" when revving - please excuse the "...." hope it makes some sense, it's just not quite there yet, No Flames this time though!

Yeah mate try removing teh extra washer, for some reason not all bikes respond well to it.

Revs hanging are a sign that the pilot screws need adjustment. Try turning them out an extra quarter turn and see how it goes.

A carb balance might also help, but it's not critical to how the bike runs.