Bike no low end?

[trademe900]

I've had heaps of NC30's but this is the first NC35... the bike seems to maybe be running rich in the low end? It's got a more free flowing silencer but otherwise stock.

Some observations:

-Once at 7k it pulls perfectly through to the redline- great top end, sounds neither fat nor thin.
-3k is pretty sloppy with the bike running particularly rich I think. Whole low end till 5k is pretty boggy and sounds fat and rich.
-It doesn't need choke to start which suggests it's too rich, is that right?

The bike has an awesome idle though. It's the most steady idle i've seen on these bikes.

Any ideas what to do?

Thanks.

[Neosophist]

Hmmm..

Does it have a standard carb setup? (airbox / filter / stacks)

First off make notes of all the settings on the carbs but id give them a 'reset to factory' treatment and go from there.

The air-screws on these carbs work backwards to the NC30 so somebody might have set them too high, also check the needles and jets are stock and there are not extra washers under the needles.

[trademe900]

Pretty sure it's all stock induction and carb setup... maybe bigger main jets to compensate for the louder pipe?

What is the low mid range fuelling like on a stock NC35?

Is an air screw a pilot screw?

One other thing is that if you are holding it JUST on the throttle constantly for a little while and then increase throttle... it will choke like it is clearing out some excess fuel and then carry on.

Everything seems to point to it running rich and low throttle and partial throttle opening... is this all affected by pilot screw?

There are no other problems and the top end is great... I'm hoping you guys can roughly pin point what it is as I am reluctant to take off the carbs :)

[trademe900]

Cammo said ''The NC35 carbs (VP series - also used on nc29, nc31 and more) are a smaller bore (30mm) which give increased torque lower down in the rev range and are a later generation design. There were many other changes incorprated into this generation of carbs to help overall performance and reliability.''

This bike definitely has less low end than an NC30... so I really hope it that is true.

So just to confirm, which way do I turn the pilot screw on the NC35 to make it more lean?

[Cammo]

So just to confirm, which way do I turn the pilot screw on the NC35 to make it more lean?

You screw it out for leaner, in for richer (the opposite to nc30 carbs!).

The nc35 carbs are lots better down low than the nc30 carbs, must be something up with yours I think. Until you open them up and have a look yourself you'll just be guessing as to what's in there.

[trademe900]

Ok thanks.

Just what are the factors that affect low end power given the main jet is correct? Pilot jet or float height which is more important? Needle? I can't quite clarify if it's throttle percentage or rpm percentage that determines use of which circuit... what I mean is- even if you are at 10k rpm and just cruising are you then using the pilot jet or is that main jet? Likewise, if you are at low 3krpm and full throttle is that pilot jet or is it main jet? Alternatively... 5krpm and just cruising... is that pilot jet or needle?

Start with 1/2 turns and see the difference? I have no idea if I'm just wasting my time with this.

Edit: I have found that the bike is much better when cold....

[Neosophist]

Yes the bike is running rich.

A cold engine and rich mixture is like having the choke on. When the bike gets warm it over-kills it.

Get the carbs off and re-set everything, see what is in there.

In regards to your throttle operation.

These are CV carbs, they work on vaccum.

Even if you are crusing at 10,000rpm, the throttle needs to be open enough to let enough air in for the engine to run at that speed, if not the engine speed would decrease.

At 10,000rpm the main jet is in effect, as the air pressure at this RPM lifts the needle out of the jet-holder to let fuel in.

Even if you open the throttle fully at 2000rpm, the needle wont come up out of the jet holder until the engine speed has increased, which will obviously happen more rapidly if you suddenly let in a ton of air.

'Gasing' it on CV carbs will show up problems with float heights and pilot screw / slow jet settings.. if it is too rich or too lean it will bog down.

But anyway, in honesty and from experience if you just start guessing with things your trying to assemble a jigsaw puzzle and your not sure if all the pieces are there.

Get the carbs off, strip them down, check the float-heights, pilot screw settings and what main jets and needles you have in there, post back on here and set them all to the standard setting.

Then you can start tuning it and people on here can advise you the best way to tweak it. Otherwise your starting from an unknown step.

[trademe900]

Real useful thanks mate.

So only pilot jet is in effect at 2k even if it's full throttle? No needle?

[skinnydog0_0]

Real useful thanks mate.

So only pilot jet is in effect at 2k even if it's full throttle? No needle?

Yer you will only be using the pilot at 2k, as there will be a lag in the slide opening and allowing the main jet to come in. so it's a kind of sliding scale as the revs start rising the main jet comes in as the vacume increases and the slide rises up and pulls the needle out of the main jet.

I have a micron race can standard downpipes and the air filter has had the paper removed. The air filter housing is standard and the flap is in place. I run 110 main jets and teh pilot screws are at 1 3/4 out. this is 1/8 leaner than standard.
But as Neo has said if your just guessing it's very difficult to get it sorted. To get it set up properly it would be best to get a guy on a dyno that knows these bikes to set it up as you want it.

[Neosophist]

Yep thats right.

At 2K rpm, things that will have an effect are.

Pilot Screw setting
Float Height
Pilot (Slow) Jet Size.

When you get the carbs off and reset / check everything clean all the carbs up to make sure there not dirty (can of carb cleaner and compressed air will do)

The needle codes are stamped on the top of the needle, also note any shim washers.

If you reset everything, get back to us with how it performs we can go from there

Just for future reference. Approx Guide

Main Jet: Top end (full throttle / 7.5k to redline)

Needle Height: Midrange (full throttle /5k-7k) - This is why I metion shims, NC30 have a hole at 7k that is fixed by raising needles

Float Height: Low end (full throttle / 2k-3k)

Pilot Screw: Idle and low rpm cruise