NC30 carby jetting - DIY guide

[Jono035]

I'm not really sure, most of the time I just figure it out by squirting carb cleaner into the holes until it sprays out somewhere else. I'm guessing it's possibly a pickup for the choke/enrichener, though.

Edit: Pull the choke wide open and spray a decent whack of carb cleaner up it and that'll tell you.

[Cammo]

the carbs are so blocked in fact they are the worst I have ever seen the jets are blocked & surrounded in a tar like substance which I am slowly clearing off what I need to know is what is the fixed tube that is shown quite clearly in the noted picture in the article above the jets I have a feeling it should be clear can anyone tell me what it is ?

Not exactly sure what it is, but yes the passage needs to be clear.

If this is blocked then other not so visible passages might also be blocked which will severly affect the carb performance.

The best way to clean all of these passages is to use an ultrasonic bath (same item that dentists put dentures into and fuel injectors get cleaned in). Not much else will do it. Try this if the bike doesn't run properly, or it might be easier to get your hands on a set of carbs in good nick.

[anp]

Hi

many thanks for the info thought they should be clear I let you know if it runs ok

cheers

Paul

[anp]

Hi Right good news & bad news

The instructions spot on for re-fitting the carbs it pays to walk away anway what seems imposible was quite easy really .. thanks Cam

It starts ok idles reasonably well considering it has a Dynojet kit fitted goes thro midrange up to 6 or 7 K and then struggles to get to 9 or 10 then thats your lot its running without the filter & airbox but the slides dont seem to open past half way I think that may be the problem so whats stopping them lifting ?

thanks

Paul

[Old Painless]

They work on vacuum iirc. They wont open fully until the engine is revving high and needs more air, creating a bigger vacuum in the intake manifold.
If your running without the airbox on stock jets it will run lean and when it gets to the throttle opening for the main jets to come in it will run lean and detonate which throws out the timing so it wont rev any more. Very bad for the engine.

[Cammo]

What Old Painless said ^

then struggles to get to 9 or 10 then thats your lot its running without the filter & airbox but the slides dont seem to open past half way I think that may be the problem so whats stopping them lifting ?

These bikes don't run properly without a filter and airbox unless you make massive jetting (and other) changes. I'm not surprised that you're seeing running issues!

Put the filter back in an airbox lid back on and see how it goes.

[samace]

Just checked my carbs only one fault found front and rear jets round wrong way. Bike was hunting on tickover and got worse when hot. also the carb clips were not tight. put in extra washer also.
will be trying out weekend now.


a very comprehensive guide for the beginer many thanks

[callboy]

Hi just wondering what the differences with the NC30 and NC35 Carbys are?

[Cammo]

Hi just wondering what the differences with the NC30 and NC35 Carbys are?

There are many differences, not many parts are interchangeable between them.

The NC30 carbs (VD series - also used on nc21, nc24 & nc23) are a larger bore (32mm) and an earlier design. It seems many pro tuners prefer these because the bigger venturi might help make more outright hp.

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.


Both sets of carbs can be made to perform very well for street or track.

[callboy]

Ty Cammo for your reply.

I have just got an NC35 with a titanium exhaust and the airbox completely removed for racing. I am unsure of the current jets.

Track conditions where I live mean that the airbox will have to be refitted, so I am going to fit the filter half back on, do you think I will have to go down a few sizes from this slight restriction?

All testing will be done on the track without a dyno.

I am also unsure of any engine mods at this time.