What make of dyno was the bike tested on ? i have a dynapro dyno and let me tell you 53bhp is a very good number for a bog stock nc30 and 12.5afr is not a rich mixture for making maximum power on a nc30 so your jetting is not far out at all , i tested a standard nc35 with 3,500mls on the clock and it only made 48bhp with a afr of 11.5 out of the honda factory ?? , dont rely too mutch on a afr reading they are very missleading and dont show you the whole story of how the engine burns the fuel mixture , look at the dyno graph and you should have a smooth curve , the smoother the climb the better, put smaller jets in and take it back and compare the curves and power output , idealy it should be done on the same day same dyno .

phil x wrote: Now who the feck suggested fitting 115/118 jets....

I think Honda started that trend...

12.1:1 is probably a tad rich, I don't think it's a massive issue.

What mileage has the engine done? Could be shagged.

This is a graph from my NC that was Dyno'd in 1993,engine had 7 thousand miles on the clock,
sorry it's not showing the bhp scale but it reads 57bhp,the run before was with a shagged chain was 12bhp down at 45bhp i was advised to replace snorkle, Take a look at jet size.



I should also say it was fitted with a full race micron ex system.

I did recently got my NC30. it's done 17k which i believe to be genuine. It's stock carbs, airfilter (clean) and exhaust (blowing slightly at rusty collect join)
As a matter of course I stripped the carbs, I had the impression they hadn't been apart before, least not by someone ham-fisted. All the screws were good, no chewed heads. Emulsion tubes in the correct place, correct needles etc. I drilled the carb slides out to 2.5mm and raised the needles by 0.5mm. It was on stock late import needles/mains etc. The carbs were spotless inside, float heights were all correct too. I have a ultrasonic tank at home and I thought I'd need to run them through but they were that clean I didn't need to bother.
Now it's too rich on choke and stalls due to flooding, knock the choke off and it stalls due to not enough revs. Riding it, it doesn't feel as crisp. I'm going to drop the needles back down again I think. As mentioned it's on the stock later import needles/mains etc

philfingers wrote:I did recently got my NC30. it's done 17k which i believe to be genuine. It's stock carbs, airfilter (clean) and exhaust (blowing slightly at rusty collect join)
As a matter of course I stripped the carbs, I had the impression they hadn't been apart before, least not by someone ham-fisted. All the screws were good, no chewed heads. Emulsion tubes in the correct place, correct needles etc. I drilled the carb slides out to 2.5mm and raised the needles by 0.5mm. It was on stock late import needles/mains etc. The carbs were spotless inside, float heights were all correct too. I have a ultrasonic tank at home and I thought I'd need to run them through but they were that clean I didn't need to bother.
Now it's too rich on choke and stalls due to flooding, knock the choke off and it stalls due to not enough revs. Riding it, it doesn't feel as crisp. I'm going to drop the needles back down again I think. As mentioned it's on the stock later import needles/mains etc

Blowing exhaust will sap a bit of power. As will knackered chain, binding brakes.

Something doesn't sound right with the carbs... on choke the needles arn't going to come into play, raising them richens up the transation area around 6000-7000rpm which is where a lot of people suffer a flat-spot.

110 is a lean jetting for the bike but by no means 'dangerous'.

Maybe you should have had the bike dyno'd first? I don't believe re-fitting the 110's and putting the carbs back to stock will give you any improvement in power.

Besides, jetting to fuel/air mixture alone isn't the best way to tune for power so dont' become too hung up by it. Many people are obsessed with this, and it's not the best way to tune for power. 12:1 isn't mega-rich and don't forget it isn't a fuel injected bike, perhaps dropping the needles slightly will lean it up some, take it for a ride and see how it feels and if you have any flat-spots.

Also 53/54hp isn't all that bad... they only made 59/60 factory figures, some dyno's will be more 'leniant' with their readings...depending on how they calculate power on these most nc30's i've seen make sub 60hp.

The 89 bike does use a different emulsion tube in the front carbs to the later bikes that came stock with 115/118 jets but I didn't change this when I upped my jet sizes and havn't suffered any ill effects, i'll have to order the tubes if still available and check the differences.

89 bike - 16165-MN4-003 Needle jet holder (cylinder NO.2&4)
90 bike - 16165-MN4-003 Needle jet holder (cylinder NO.2&4) (VDE3D A carbs)
90 bike - 16165-MR8-780 Needle jet holder (cylinder NO.2&4) (VDE3D B carbs)
91 bike - 16165-MR8-780 Needle jet holder (cylinder NO.2&4)

Needles were same through all years as were rear emulsion tube (Late NC24 part).

fwiw my bike is a completely stock 89 bike, I drilled the slides to 2.5mm, havn't raised the needles, standard system that isn't blowing

Starts and idles like a swiss watch, has dropped a bit colder lately so need choke more often but it runs fine on the choke for 20 - 30 seconds until I can knock it off and warm it by throttle. I also don't have any flat-spots, didn't need to raise the needles as I wasn't wasn't having the issue after re-jet.

I'll get it dyno'd after I repair it but i'm sure it's making more power now, there are no flat-spots, top-end is more and it 'feels' like it pulls harder. Could be wrong with the numbers, depending on the price of the dyno i'll try and do back to back runs with 115/118 vs 110's all around.

Either-way i'd much rather ride it with the 115/118's in it as it's smoother. There is no soot accumulation on the end-can either so it can't been running overly rich, the plugs are also a lovely golden tan colour.

Don't despair, you'll sort it!

While it may seem like blaming the carb mods is the thing to do it sounds like you have more problems, perhaps bad sealing float somewhere or incorrect float-heights (how did you check / adjust these?), something sounds amiss with the carbs with it stalling on choke.. main jets shouldn't be in play.

Lots of people have gone to 115/118 setups on a standard bike without issue (including all 1990 > bikes). 115 / 118 shouldn't make it mega-rich and really shouldn't affect your choke-setup.

What are the pilot screws like? are the o-rings and washers present and correct?

Also check for brake drag and chain condition.

For total piece of mind you could put it back to stock and dyno it, I wouldn't expect anymore power though.. try to work out why it's dying on choke now and you might have better results.

FWIW though, one guy on here's old nc30 only made 46hp, after a long time at the dyno... fuelling was pretty much stochimetrtically perfect throught the rev-range too.. even when richened up or leaned off it didn't make any more power. 53 i'd be happy with!

Since you describe ill sounding bike though there could be a few more hp's in there

I had a similar issue with it running mega rich, was going to check the floats and the choke system. That was before I smashed my wrist up.

Hi, & thanks for all the feed back.
The dyno I used at Quill was a 'Dyna pro'.
The reason I went to the dyno was just as a check - I had a gut feeling the bike was a bit rich & was not great on fuel but overall runs very well. Personally, I'm not fussed about trying to squeeze the last 1/2 hp out of the bike - it's a sunny day toy for me, I like my bikes to run a clean exhaust & return good fuel consumption along with a nice linear power delivery.
Maybe 12:1 isn't mega rich to some of you guys but from past experience I have gained power & improved fuel consumption by running closer to 14:1 from low 13s (3/4 hp & 5-7 mpg ave), I'm not however suggesting that the NCs respond the same.

As always, it's a learning curve!

Phil

Not sure where the 12.5-13 value comes from as when you mathematically work out air/fuel mix for perfect combustion it comes out closer to 14.6 IIRC. Assume its down to inefficiencies in the fuel delivery.

Quill..as in, we have a load of shit twin stacks?

Have they any graphs from them?

Their normal cans etc are great...up to a point.

When I got mine the seller told me it started without choke, but saying that I bought it 3/4 weeks ago and the seller only had it a month over the summer, so it wouldn't need much choke.
Once I drilled the slides and raised the needles on choke in the mornings (it's cooler now than when I got it obviously) you can visibly see black smoke and smell it- rich! Knock the choke down and the rev's won't allow it to idle. Warm it idles nicely at 1500. There's only a slight blow. I'm tempted to balance the carbs, tho they're not far out TBH.
I may well drop the needles back and try it again, I hadn't ridden it much before I changed the settings, I've done 500 miles on it since in the last 7 days. . . . :-)