NC30 carby jetting - DIY guide

[bobby]

Good instrutions, on a nc24 the 2 holes in one you drill to 2.5mm are both next to eachother, so does it matter witch one you drill? where do you get the little washers from to raise the needle and the bowl gaskets? thanks

[pauliealdridge69]

type "rick o price list" in the search bar

[duanebray_08]

Ok had my nc21 carbs off as my bike wasn't running right. I checked the emulsion tubes were in the right place and clear of crap. I then checked the pilot jets which were standard and clear but my main jets were all 115. The airbox and filter are completely standard and so is the exhaust apart from a Scorpion pipe. The problem I have is the bike redlines in 1st, 2nd and 3rd but in 4th it stops dead revving at 10k if I put it in to 5th the revs drop to around 9k dead and I can try and give more throttle but nothing happens. Could this be due to the 115 jets starving the engine at high revs? I have tested the compression which is good and I have tried new coils with no success. Any help would be appreciated. I'm thinking of going back to the 112/110 standard setup and seeing if this help. Thanks in advance.

[vfrman]

Or it could be your fuel tap restricting the flow of fuel to the carbs. This is a big issue in race bikes that spend a lot of time at WOT. There is a HRC mod where you remove the diaphram from the tap, but this can cause flooding problems if your carbs are leaking at all through the floats.

[duanebray_08]

Never heard of it? I'm quite a newb lol. Is it straight forward?

[beaunc30]

HI, i have a 1989 nc30 import and have just changed the jets from 115f and 118r to 118f and 120r im running standard exhaust with art can, the bike ran ok before but had a flat spot at 6-7,000 i also put 1.0mm washer on the needles and drilled the hole out to 2.5mm took out pilot jets and emulsion tubes all in where they should be and no blockages, i also cut out an envelope in the airbox tray and covered it with a mesh to get a bit colder air in, put all back together and started fine, next day went to put fairings back on but had a petrol leak from left front carb inlet took carbs back off and left front cylinder full of petrol. cleaned out checked float wasnt stuck but all seemed to be ok put all back together and took out for a blast all seemed good then about a 2mile down the road thought i was running out of petrol so put it on reserve but still no change, limped home took everything off again incase carbs where not seated properly then battery went dead grrrrr, charged battery then it started took for a blast again seemed a little better, doesnt tick over great needs to be at about 2000rpm to tick over nicely but after a blip of the throttle it either cuts out or revs to about 3-3000 rpm, the power from tick over to about 6000 rpm is very spluttery but once at 6000rpm it runs and pulls better than it ever has any info would be great the only thing i didnt do when carbs where off is the float height, sorry for such a long write up but thought it best to give all info
scott

[karikeo]

excellent work
I worked my but instead of occupying washers, plastic deal with which made ​​the plastic washers was 0.5
great job greetings from chile south america

[Cammo]

If the float's aren't stuck then carb fuel leaks are usually due to the float bowl gaskets. I'd recommend fitting a new set of o-rings from Rick Oliver, 6 quid for a set of 4. His stock list is here: viewtopic.php?f=22&t=26174

i also cut out an envelope in the airbox tray and covered it with a mesh to get a bit colder air in

This sort of thing is known to cause running issues, these bikes are very sensitive to airbox/induction changes. Highly probable that this will be causing dramas.

[beaunc30]

thanks for your reply i did change the float bowl gaskets, it was a petrol issue i didnt have any lol

[speedy231278]

Something I've been pondering over for a little while.... in essence the 30 and 35 have the same engine, I think the only differences are a very slight change in the cams and the exhaust valves. The carbs of course are completely different. Notwithstanding, why is almost universal practice for the 30 to have jets a size bigger in the rear, while there's almost no reference to the same practice for the 35? I think one poster on this thread mentioned trying it, but went back to having the same size all round. Is it possibly because the 30 has five holds in the rear emulsion tubes and four in the front? I presume this richens up the rear cylinders in relation to the front ones. Is this due to them being buried in the back of the bike and potentially running a bit hotter? Makes me wonder if Honda decided it wasn't actually an issue when they evolved the 30 into the 35, or is the different position of the bottom hole in the emulsion tubes of the 35 a different way of achieving the same?

Edit: having looked at the pics at CMS, it appears that on the 35, the tubes with the bottom hole lower go in the front carbs, and the less spaced out ones go on the front. Is that right? I'll check with my spare carbs this evening, but that seems a little odd as well. However, didn't someone say the 30 runs a bit lean in the middle stock, and the 35 a bit rich? Would that be anything to do with the different tube arrangement between the two?