So if you do this type of setup then it would be better controlled and easier and more accurate an equal for all carbs because there would be no turbulent air affecting the intake of air ?

Standard air restricter:


Modded for pipe restricter:


Fitted kit:


Adjustable Nob to control air:


V4 setup with filter to aid intake:

Neosophist wrote: Still the HRC system uses larger than standard jets, i'm guessing the shrouding like you said is to keep power delivery smooth.

If you don't restrict the air jets when using the hrc nc30 carb setup (and subsequently using 160+ size mains to give a good mixture at WOT), there will be a massive midrange hole that the bike will have trouble pulling out of.

The nc35 carbs use a different air jet setup to nc30 carbs.

I know of two NC29's running a restricted air bleed in OZ. Allows you to run standard main's and needles on a race engine.

Only just found out why it works thanks to Stickshifts explanation.

nice one.

This diagram shows what is happening when you restrict the air jet (taken out of John Robinson's handy book 'Motorcycle Tuning - 4-Stroke'):




The only real benefit of restricting the air jet is as Greggo said above. You can get away with smaller main jets to suit the induction setup when larger main jets aren't an option due to too much air entering (e.g. ram air, nc30 hrc setup). It will avoid massive flat spots caused by the jump in fuelling between needles and mains.

If anyone has taken the airbox off an nc30, fitted very big jets to give good/perfect fuelling up top and expected it to run perfectly then they're mistaken. A huge midrange hole will result that can't be tuned out unless you restrict the air jet. I picked up my last cheap trackbike because someone had attempted this and then given up and passed it on!


Basically, restricting the air jets will avoid this problem (although nc35 carbs don't seem to suffer the effects as badly as nc30 carbs, ram air will still create havoc with standard fuelling techniques!):
http://www.400greybike.info/newforum/vi ... 24&t=13464" onclick="window.open(this.href);return false;


Some tuners block the air jets off completely, although in theory having some air pass through should help with emulsification of fuel into the airstream, I haven't tested the difference though (probably not a world of difference on a racebike).


I certainly am no expert on the subject but have done what's needed to get my (and others') racebikes to fuel properly. You can get the fuelling very near spot on by tuning the air jet and main jet, then you only have the easy stuff (pilot jet, needle height/taper, pilot screw) to go! I'm sure that most tuners will agree that mains and air jet are the first things that should be matched for top end fuelling.

G-MAN wrote: Fitted kit:


Adjustable Nob to control air:

Those setups (factroy Pro?) are a neat idea, but I just set and forget the air jets in my racebike.

I do change the main jets though depending on weather conditions.

Stickshift, I found that many moons ago on that site but it doesn't seem to be there http://www.motorcyclecarbs.com/index.cfm" onclick="window.open(this.href);return false; still have the web page saved, here have a look

G-MAN wrote:Scoops, how much did you fork out for the setup ?

Why is that moto of yours making less power than wen you got it ?

I beleave this is your spec:
Engine:-
Freshly Built New.
74 bhp. RLR Stage 3.
RLR Ram Air System.
Carbon Fibre Enlarged Air Box.
Gas Flowed Heads.
Modified Inlet Ports.
Skimmed High Compresion Heads.
NGK Race Plugs.
Race CDI Ignition.
Kit Alloy Top & Bottom Rad.
Sparco Rad Hoses.
Mercury Full Race Twin Hi Level Exhaust System.
Titanium Cans
Carbon Engine Armour.

That bike only made 58 horse power for me

Drunkn Munky wrote:Ok now im confussed........you brought one of aly's 74bhp 35's....and now you've changed to smaller jets and getting 69bhp.....why?????? or am i missing something here?

See above post

Stickshift wrote:This diagram shows what is happening when you restrict the air jet (taken out of John Robinson's handy book 'Motorcycle Tuning - 4-Stroke'):




The only real benefit of restricting the air jet is as Greggo said above. You can get away with smaller main jets to suit the induction setup when larger main jets aren't an option due to too much air entering (e.g. ram air, nc30 hrc setup). It will avoid massive flat spots caused by the jump in fuelling between needles and mains.

If anyone has taken the airbox off an nc30, fitted very big jets to give good/perfect fuelling up top and expected it to run perfectly then they're mistaken. A huge midrange hole will result that can't be tuned out unless you restrict the air jet. I picked up my last cheap trackbike because someone had attempted this and then given up and passed it on!


Basically, restricting the air jets will avoid this problem (although nc35 carbs don't seem to suffer the effects as badly as nc30 carbs, ram air will still create havoc with standard fuelling techniques!):
http://www.400greybike.info/newforum/vi ... 24&t=13464" onclick="window.open(this.href);return false;


Some tuners block the air jets off completely, although in theory having some air pass through should help with emulsification of fuel into the airstream, I haven't tested the difference though (probably not a world of difference on a racebike).


I certainly am no expert on the subject but have done what's needed to get my (and others') racebikes to fuel properly. You can get the fuelling very near spot on by tuning the air jet and main jet, then you only have the easy stuff (pilot jet, needle height/taper, pilot screw) to go! I'm sure that most tuners will agree that mains and air jet are the first things that should be matched for top end fuelling.

I'm with you now :-)

But with my standard airbox and filter I don't have sufficient air to need blockin the jets off :D

Finially got around to getting the bike dyno'd. It has a full tyga system with everything else std. Ended up going from std 118's to 112 dyno jets(around 115std) Ricks advice. And she is fueling perfect putting out 58.3bhp, only slightly on the rich side. Thanks a million Rich. They recon I could still go one size smaller on the main jet. So after all the advice to change to a bigger main jet, it looks like smaller is better!