NC30 carby jetting - DIY guide

[Drunkn Munky]

I dont think you drill UK slides either, just jap ones

[CRM]

uk jetting is the wrong way around comapred to jap spec carbs / emulsion tubes so it was correct in the first place.
and dont even think of drilling the slides either.
going against the grain here i have only found it make things worse on any import set of carbs i have had. if everythings right then there is no need to drill to mask the problem.

[paul.s]

no its a uk bike and it had the 122 jets in the front carbs and 120 in the rears according to the haynes and earlier in this thread it should be the other way round

[Neosophist]

uk jetting is the wrong way around comapred to jap spec carbs / emulsion tubes so it was correct in the first place.
and dont even think of drilling the slides either.
going against the grain here i have only found it make things worse on any import set of carbs i have had. if everythings right then there is no need to drill to mask the problem.

115/118 in my JDM bike, no extra washers but did drill the slides.

Didn't find it made any noticable difference but the bike runs like a swiss watch from start to the red-line.. no bogging from idle on any range of throttle and no-flatspots either.

Smoothest non-FI bike i've ever had.

[baptiste nc30]

good morning everybody,

I have cabs problem on my race bike, she has jap full stock carbs

I recently bought carbs on ebay to replace them or to fix my carbs problem.
I expected to find different carb main jet but i found totally differenet slides, jets, needles etc...

The slides are made of coated steel with two holes at the bottom, the vaccum diaphragm is linked to the slide by a red ring, the needles are thicker than jap at the base, without 0.5mm spacer at the top and finally the jets are 120.
Is anybody know where are they from? are they english or french spec?

which carb setting is the best with stock air intake and race exhaust can?
it tried the new carbs on my bike and it's not better, i still have bad throttle response, with bad rev climbing. I'm a bit lost in my bike fixing :-).
Please help...


thanks a lot.

Baptiste

[CRM]

sound like UK spec carbs.
make sure the emulsion tubes are the correct way around, and other factors make a big difference too like valve clearances, and ensure the carb rubbers are new or in good condition too

use a genuine air filter every time - i have had some big mid range holes with a 35 using a aftermarket filter.
and for a race can, then go up one size allround as a start and go from there.

So start with standard settings, do not drill the slides, and if you can explain the following

Does it start easily from cold with or without choke ?

Does it run better when cold or warm ?

Does it rev clean between x rpm to x rpm ?

Does it stutter at x rpm ?

Does it feel better if you ease off the throttle slightly at 9k+ rpm ?

The more information you can provide the better we can help diagnose.

[baptiste nc30]

Thanks a lot,
I will try to be as clear as possible,
My air filter is clean, my spark plugs are new, my carbs pipes are new as well. I checked the valve clearance 1 month ago.
I tested my jap spec carbs since i bought the bike. the result is:

Does it start easily from cold with or without choke ?
-- always start easily with choke, rev perfectly at the idle speed (1k)

Does it run better when cold or warm ?
-- it runs better while warming
Does it rev clean between x rpm to x rpm ?
-- run very well from 8000 to limit, throttle fully opened
Does it stutter at x rpm ?
-- it sutter at iddle spped while throttle quick opening, and then at from 5k to 7k
Does it feel better if you ease off the throttle slightly at 9k+ rpm ?
-- i don't think so, not a 9k but yes when it slutter.


I thought that i could change the carbs for better ones and i bought EU spec carbs, i checked jets, needles, floats heights etc...
New diagnose:

Does it start easily from cold with or without choke ?
-- still start easily with choke, rev perfectly at the idle speed (1k)

Does it run better when cold or warm ?
-- it runs better while warming but very bad running with many holes while throttle opening
Does it rev clean between x rpm to x rpm ?
-- seems running at high rev
Does it stutter at x rpm ?
-- it dies at iddle spped while throttle quick opening, and then at every rev if i throttle to much (1/4 throttle)
Does it feel better if you ease off the throttle slightly at 9k+ rpm ?
-- yes, need a fine throttle to rev properly.

Actually, i would just be sure that i have only carbs problem and not electrical (CDI) disease. If the Nc30 is highly sensitive to carburetion, i should will bring the bike to a mecanician, isn't it?

Thanks a lot.
Baptiste

[CRM]

Sound like the main jet circuit is just fine so checking the low speed running, pilot jets and needles and emulsion tubes are correct and in the correct order.
Another thing to check and check again is the float heights, these make quite a big difference on the NC, and once i learnt how to set them and what difference it made 1mm either way it was remarkable.

See where what i did
viewtopic.php?f=22&t=26178&p=186207&hil ... ht#p186207

ok thats for the RVF, but use an old plastic business card cut similar, and measure that way. If they appear out (using the card ensures both sides of the float are level with each other unlike a ruler) then adjust accordingly.
try to get it as close to standard settings as possible.

one thing it sounds like your main jetting is spot on so dont worry about changing those.
Just make sure the slides are not drilled, nor there are any extra washers under the needles, and the springs are standard too.

Its a pain to check, but once right will transform the bike.

[baptiste nc30]

OK,

I didn't know that the floats height was so important. I will check that as soon as possible. Please can you confirm that there are 0.5mm washer on the needle for the uk spec carbs because I don't have.

I checked the jets and emulsion tubes: 122 jet/4 holes tubes in front and 120jet/5 holes tubes rear.
I checked the pilot screws: 2.5 to 3 turns. it is a bit high isn't it?

cheers

Baptiste

[V4beermonster]

hey guys just bought and fitted a system from vfrderek/porndog viewtopic.php?f=17&t=32730 have alook here any suggestions on jetting and setup of the carbs? system sounds awsome