To perform any kind of jetting or jet changes you need to know what jets affect what operations in the carb and then you need to gauge what the engine needs. This will be done by plug reading and seat of the pants unless of course you have access to a reliable rider and circuit to check lap times or a dyno.
If you are a normal human and only have your fists, brains and toolkit you can use the first method described. Why fists, you'll need those to hang on to the handle bars. A second and most important factor is choose a day where the temperature and humidity most suit your average riding , If it is for racing simply log the ambient temp, track temp if you like for your tyres and humidity then you can work your way to better tuning every meeting at that track.
The first thing to do is balance the carbs so if you thought you had fortunately missed the first page you have not and need to go back and do it. If that is done then you are ready to do some jetting and the first thing you will need to do is fit a new set of plugs so we can do a plug run. If you cannot get a straight section to open it up on and have to ride there take the plugs with you and a spanner for plugs, you can take the main jets and tools needed to change them and don't forget a rag to soak fuel when you drain bowls to change main jets.
Once plugs are fitted we need to ride it and I mean ride it, full throttle all gears (well from second or third at least ) to red line going up gears to the highest gear you have the opportunity to go to, though not essential. At this point you must cut the kill switch with throttle still open and pull in the clutch, effectively killing the motor and stopping it dead at full revs then braking slowly to a stop and I mean slowly the bike has no engine braking or gyroscopic engine stability, only the wheels so don't smack on the brakes and don't release the clutch and run the motor it will wash the plugs and you must read them at the point the where when you hit the switch at full speed.
Above all be careful when doing a plug run remember you are riding and tuning so don't forget the riding part and don't go in your overalls, suit up. If restricted go to third or fourth gear and kill it, this will still give a fair reading at the plugs.
Once the bike has come to a stop remove a plug and check the colour. What you need to look at is the white centre insulator, inspect it for the colour in comparison to its original white if it is pure white and there is light gray body it indicates lean condition but it is not too far off the mark. On a bike plug you only need to look for a small quantity of the fuel residue colour if it is leaded then you will note a light tan on a road bike and for racing more like a bone colour, If you are using an unleaded then you will have a grey dusting affect this also applies to avgas although it depends, some blend super and avgas with methyl benz and synth oils so this gives different colours again. I merely say check for the amount of burnt fuel residue left on the plug, whatever fuel you use it will leave a small amount if it is burning correctly, even the most efficient engine and plugs wont burn it all.
If it is rich it will just be heavily coloured if it is lean it will be barren and white. If the nose cone is shining or polished it is too hot it must always appear a dull matt finish on the nose cone even when lean it will just be ivory white if you see grey spots or flakes appearing on the outer metal edge of the plug. Danger Will Robinson that is piston material, TOO hot .
Anything that is not meant to be there, or that there is excess amounts of in the firing mixture will condense against the cool edge of the plug casing and oil or lead will build up there fast but in your new plugs for the jetting job we are looking for a single fuel reading so this test will not show up much more than lean or rich unless the motor is really worn. You should check all the plugs first time round to make sure all is OK engine wise and that you haven't got a wonky carb, float or choke if you feel that you can confidently remember the plug colours then move on if not fit another set and you can compare them you can keep them for your next set of plugs anyway once you have read the plugs and or noted output on dyno or backside.
You need to decide whether it needs more fuel if the plug is dark go lean if it is distinctly light go richer you do this at the main jet located in the base of the nozzle in the bowl chambers. You need to do all the carb's main jets. You need to remove the bowls or if you have access caps remove them and refit a smaller or larger main jet it simply screws in and out then refit caps or bowls , turn on fuel, start and check for fuel leaks then repeat plug reading test as above by riding the bike as described. Watch for a change in power particularly in late revs and then chop it and stop remove the plug of your choice and check it. Note if you feel a drop in power stop straight away and go up one richer do not persist with a lean condition you may cause damaged if you ride it. If you have set up camp somewhere idle back there to change the jets or do it on the spot of so equipped. ( motor cyclists often are )
Repeat this until you are satisfied with colour and peak power. Next we will determine whether the bottom end is ok or the roll on of the throttle.
For most carbs on unmodified bikes you will not need to do more than main jet and mixture screws, maybe a needle clip changed one spot with exhaust or air box changes. This document assumes you wish to jet the lot so read what you need but don’t leave too much out.
After you have done the main jet settings we move down in terms of jetting to the part that affects lower end power, you may imagine we move to the main air jet which affects the main jet range but as the bottom end is where the engine starts in Revs the result of its mixtures may be overlapped into the upper operating range so due to this we move to the pilot system. The main air jet is not generally adjusted unless there is a radical altitude variation or a change to intake volume and speed due to engine mods.
Likewise the slide cutaway angle which faces to the outside of the carb affects the point in air speed when main bore fuel flow is started and the mixture starts being controlled by the needle taper in the bore of the main jet nozzle, adjustment of the cutaway is by changing the angle or slide number this, as with air jets, is only required for considerable air flow changes. Changing the point at which fuel starts being metered from the main bore is done by lowering and raising the needle in the slide, you will note it has a clip and notches in the needle.
If the clip is fitted to a lower position on the needle it will open the needle earlier when the slide is lifted thus allowing more fuel at the same slide position. Further opening to full throttle is controlled by the needle taper, adjustable by using a different taper needle. The needle comes with a number stamped on it. When the needle is fully withdrawn you are operating on the main fuel jet and air jet. There is also adjustment values for the main jet nozzle or tube, you will note it has small holes on the side of the tube, this is where the air enters to mix with fuel rising from the main jet and then out into the air stream the nozzle like the air jets and cutaway are largely set and forget and will control the range of affect of the system they operate on. In the case of fuel jets it will control the actual mixtures through that range IE if you need more for longer over a power curve due to air speed or port / cam timing mods you will need to change air jets to lengthen the effect of the main or the mid range needle taper and not so much but even the duration of the pilot jets effect with the pilot air jet which I might add is usually a fixed jet.
If you need more fuel at the curve you would change the fuel jet or needle taper or the mixture screw. So if you have a broken up or lumpy response by that I mean good and bad acceleration spots try adjusting the needle positions and this will indicate the direction you need to take with air jets once you have a more uniform acceleration you can adjust fuel mixtures by changing pilot fuel and screw settings then the needle position and taper and if necessary main jets again to fine tune. As I said start at the balance then do main jetting then move to pilot and needle positions these will indicate your deficiencies.
If you adjust the idle mixture screws in and out counting the turns and test off the mark from idle and starting also blip it in neutral and clean out flatness with mixture screws then riding off the mark and slow cruising at walk pace to see if it falters you can determine by then counting the turns on the mixture screws if it likes a lot you might want to move up a pilot fuel jet size then try it again until it feels right and the mixture screws are close to original specs which you will note in the manual. The idle screws settings are expressed in turns out from base.
Next we will move to the next range up and test this by cruising at walk pace and accelerating at varying rates of acceleration try off the mark using the clutch from stop also. Then try short shifting at low revs into second and accelerate with a bit more load doing this and in between lowering or raising the needle or vice versa for the clip position until you are satisfied, it must be a smooth transition from idle and cruise at all throttle speeds quick and slow, then noting the needle position if it is high it needs more fuel earlier and if the pilot does not correct it you will need to change the needle or cutaway but as I said the cutaway is virtually pre-setable if you put a bigger carb on a small bike you need a larger cutaway to have the air speed at the main nozzle at throttle opening.
The cutaway adjustment is in line with air speed changes so move to needle tapers for further adjustment, if it is a serious shortage or excess at mid range roll on you will have to select a different nozzle this is similar to an air jet adjustment and will affect the point in air speed at which the main bore operates.
You may end up needing to decrease the main air jet size to increase the spread of the main jet operating curve but remember you can spend a long time jetting and it will only be spot on if you do the adjustments one by one and read the results then be prepared to go back over your tracks to reset other settings.
It is a juggling act but most of the carb's can be set such as nozzle, needle, slide cutaway and pilot jets then out at the track or next tune you only need the mains and the main air jets can be used to play with top end curve if you like and mixture screws to set easily then if you have multi cable carb's needle heights are a snap. Also take note that when you have done jetting and tunning you need to have the mixture screws at or close to preset turns and needle height at centre position, if the carb operates properly and your jetting is correct you have some quick adjustment range available at your screws or needles for fine tuning after you have set your main jets for the session/day/race/season whatever you like or how ever many times you can be bothered tuning. If you leave the screws in or the needle all the way up to get it right, when you need more you wont have any more adjustment and you will have to do the rest of the jetting then so do it now.
	In a CV carb the same applies as with a slide controlled carb in respect of jet placement and adjustment but do not adjust the slide cutaway, it can be done but don't mess with it as it is crucial to the slide operation. And if you note it is hardly noticeable in comparison the carb at the top of this page.

If you intend to use a carb on a different machine to original then you need to consider whether it is operating in a higher or lower air speed, I suspect a lower air speed so you will need to adjust the size of air jets including slide cutaway and nozzle size plus the fuel jets to cater for lower air speed if you only do the fuel jets you will have a very lumpy carb or in power a very unpredictable power curve at throttle on, IE all or nothing. If you are prepared to do the work you would be surprised at how big a carb you can run retaining a good bottom end throttle response. If you intend to make a radical change requiring more fuel you may need a larger fuel needle seat inlet size also.

As an example in 1981 I raced a production LC 350 Yamaha w/cooled, sick of std moving to improved touring I decided on porting , chambers and carb's I picked up a pair of 36 mm Mikuni's off YZ's from a wrecker then after TZ spec porting and chambers and knocked about 5mm of the head then I removed the intake manifolds, I mean cut them off to the barrel and rebuilt manifold blocks using 10mm plate alloy. This allowed fitting of the YZ six petal reed blocks with steel reeds which replaced the standard four petal reeds, see the regs where "original engine appearance" so a little cosmetics added.

This is where a had my sharpest carb tuning learning curve I knew the reed block mod was good I got it from a multiple title late 70's Australian RRC winning motor I had the luxury to sit around and measure bits of. So far I had recreated all the sizes including head CC and carb sizes but it ran like a dog down low and then wheelies all over the place. But after much asking , learning, trying, testing and adjusting it ran like a song, it had the legs on the straight and it idled nice although I ran no idle, everything in between was spot on I even had to put bracing in the swing arm I was impressed I was 22. Then of course I had a couple of twisted and broken cranks whilst enjoying my new found power I cured that but that's another story.

So that’s it for now as usual I will update the pages. There is a limit to how much time I can spend on each page as I have to create pages for other subjects also. This is enough information on the subject thus far to get you started and give you some tips and as I rotate and update pages more of interest will be added to all.