carbs jetting

on the fuel/exhaust system everything is original except a full Delcevic with an oval can of 350mm length.
upstream the baffle i added wire mesh, it was too loud to me
pilot screws open 1 1/2 + something. (no popping)
the bike runs OK.

yesterday i change the slow jets from the original Keihin, marked 38S, to Keihin 40
took a ride.
had to unscrew the pilot screws to 2, the bike bellow 4000rpm was not pulling at all, and later to 2 1/2 to stop popping.

the bike runs OK, pulls a easier, that's the feeling is have.
takes shorter time at 4rth gear from 60 to 100Km/h

about fuel consumption i have nothing to say, ambient temperatures of about 4C maximum are not for looong rides, later on.

what is the suffix "S" stands for (stock, special, small, sport, standard)? 
are the 38S bigger than the 40 ? 
any ideas ?

If the bike was running fine, why change the slow running/idle jet?
Yes 38 is bigger than 40.
S is for sport I believe.

thank you ANDYC

i'm looking to improve the response between 4000 and 6000rpm somehow 
i'm looking to be ready with the carbs before go to a free air filter
i have nothing else to do on the bike & never touched the carbs (except cleaning/balance)
i have the time/area/skills (i want to believe so..)/budget
i have nothing else to do during this winter

this is the link with the Keihin slow jets.
https://www.keihin-na.com/assets/1/7/jetlist.pdf
our type is the very first on the left column, page #1 
N424-21-  

if 38>40 then we are at the end o the range, bigger than 38S should be the 35, sound strange to me

for the Keihin main jets the number of the jet is the mm of the jet/100, say 122, thus 1,22mm 
for the Keihin slow jets should be the same ..?

The slow jets won't have much effect in the range you're trying to change. That would be down to the main jet and needle position and taper.
Sorry for my error, 40 is bigger than 38.
Not all jets are measured by the diameter of the hole, some companies size their jets by the amount of petrol that they flow per minute. As a 2mm hole will flow much more than twice the amount a 1mm hole would flow. 
Moving to a 'free air filter ' would change the characteristics of the carbs completely so you're wasting your time sorting the jetting out until then.

https://cbrforum.com/forum/cbr-600f2-16/re-pilot-jet-whats-diff-between-38-38s-136908/

from another Honda forum.
i have to check these holes.

ANDYC, please show me where to buy needles with different taper
or, how much to raise the existing

thank you.

Many needles have a number of grooves so you can adjust the height up or down. 
Unfortunately the cb500 ones don't,  however it can be raised by using a small washer under the head of the needle. Don't go too wild with the washers as they do make a difference. As a rough guide I use one 0.5mm washer as half a main jet size.
Take a look at my track bike thread, it may give you some ideas.

clear ANDYC ! thanks !


I'll try to find something else to do this winter...

so to understand not to look for different taper needles, just try adding washers.

once again, thanks !!

Looking for the correct taper needles would drive you mad. 
If you change the needles, then you will need to change the jetting to suit them and possibly the main air jets(which aren't changeable on these carbs).
So at least decide which filter system you want to use as each individual system will require a different approach to the fuelling. 
In reality unless you are seeking big power gains (which is an expensive exercise) the carbs and airbox are best kept as standard.

Thank you ANDYC, i'll follow your proposal, stay at the original setup

about the exhaust system: the original gets rusty and sounds funny.

what about when adding an aftermarket one, a full Delkevic with an oval can of 350mm length, leave the carbs normal ?

If just changing the exhaust, try the standard jetting before doing anything else. If you're happy with it leave it alone, otherwise go up one size main jet.

yes, I am, years, with the Delcevic and the standard jetting.
Trying to be happier I started with the slow jet, the birth of this topic.

you mention to go up one size with the main jet.
Please make it me clear: the main jet is bolted on the main jet holder, a well/pipe/tube where the needle "works" moving up/down
the upper the needle,  the bigger the area/ring created between the needle (due the taper shape) and the main jet holder (well/pipe/tube)
but still the same area doesn't matter the size of the main jet bellow.
This is valid and via versa, when the needle moves down, smaller area/ring between the needle and the main jet holder.


following your proposal what will give a bigger main jet? 
at Wide Open Throttle, will give for sure, out of WOT range what are the gains ?

You are correct about the relationship with the emulsion tube and the needle, and yes the main jet is at the bottom of that tube. 
A larger main jet will still make a difference as more fuel will get past the needle at any given opening as the fuel mixture getting past the needle will be richer. Air is introduced into the emulsion tubes to atomize the fuel so it burns more efficiently than if it was just in a liquid state. So the change in main jet affects the whole range other than the idling bit.

yes ! emulsion tube, the correct phrase/word !!

indeed, the emulsion tube has 12 small holes, thus air should be driven somehow to these emulsion tube's holes, to atomize the sucked (through the main jet) fuel.
this air should also be "dosed" (be proportional) to the open/close of the throttle.

where from comes this air ? these carbs have no air jets !

Yes they do.

fixed ?

unfortunately yes.