Jetting info grabbed from another site

[Suzukidave]

Name It Affects
1) Pilot jet 1/16 to 1/4 throttle
2) Air screw Idle to just off of idle (not the idle screw)
3) Jet needle 0-1/2 throttle, work with the needle shape first, then the clip position
4) Needle jet 1/8-3/4 throttle, also called nozzle
5) Slide cutaway 1/4-3/4 throttle, the angle of the cut affects air intake (high-dollar item)
6) Main jet 1/2-full throttle

1) Pilot jet - Affects mixture from idle to 1/3 throttle opening. The pilot jet meters fuel to the "bottom end circuits"
2) Air screw - Meters air to pilot jet. It is usually located near the back or air box side of the carb. Turning in clockwise will richen the pilot mixture. Turning out, counter clockwise, will lean out the pilot mixture. Average setting for most two strokes is 1 to 2 1/2 turns out. Refer to owner's manual. If the airscrew is set to less than 1 turn, it needs a bigger pilot.
3) Needle - Affects the mixture from 1/4 throttle to full throttle. The needle is in the leanest position when the clip is on the top, and richest on the bottom. The needle calibrates the fuel to the change in throttle valve (slide) opening. The further down the needle is, the later the main jet comes on and the leaner the mixture at that point.
4) Main Jet - This circuit affects the mixture from 1/2 throttle to full throttle. This is your full blast top end circuit. This circuit is most accurately tuned by checking the plug for the correct color, sort of mocha brown.
5) Float/Float valve/Float level - Your owner's manual has the correct level and procedure for calibrating your bike. Here are some symptoms that would indicate the need for float adjustment.
A) If float level is too high, the float bowl overflows out the drain hoses, and fuel often blocks the air passages that allow the carb to de-pressurize. This causes a bog, or hiccup over large hits.
B) If float level is too low, the engine starves for fuel off idle, causing a "boooooowang" sound very similar to a pilot jet or airscrew set too lean.
Every component overlaps the throttle range of one or more of the other components. Most people only change needle clip position, and pilot/main jets. Most people check jetting by looking at the plug or the exhaust spooge. We will attempt to jet by how the bike sounds and feels in response to throttle input at different rpm starting points. We won't really address the cutaway because of price. Not too many people can jet a bike right the first time; all jetting is trial and error, because every bike is different.
How to Jet:
1) Mark your throttle housing and grip in 1/4-turn increments. Use a marker, razor blade.
2) Now get the motor to operating temperature by riding around, away from the pits.
3) Once the motor is warm, ride in 2nd and 3rd gear from the low RPM to high RPM. This puts a good load on the motor and is an accurate test of performance.
4) Now try to locate the throttle opening at which the problem exists.
To develop your skill at jetting, you need to experience too rich and too lean with every jet (pilot, needle diameter, needle clip, and main jet). Only after you feel what too rich and too lean is will you be able to jet your bike perfectly. One size smaller in the main or dropping the needle a position or two can often make a huge difference in performance! Keep in mind that one area (i.e. throttle opening) can be rich while another is lean. For example, the midrange can be lean, which will cause a miss, but the top end can be too rich, which would cause blurbbering.
Step 1: Main Jet
The main jet controls the mixture at full throttle. It is possible to foul your plug if the main jet is too rich (but only if you're running at or almost at full throttle). Notice that we are talking about throttle openings here, not RPM. Other jets have negligible effect at full throttle.
Your objective is to get an understanding of the mixture at full throttle (wide open) operation. You need a long up-hill straightaway for this test so you can be in the top gear with the engine under load and running up in the upper RPM range.
If you hear pinging or missing, it is running lean; go larger on the main. If full throttle causes gasping and poor pulling at mid RPM’s, it is again an indication of running lean, so go larger on the main.
If the bike runs clean, select a larger main jet until you find the jet that causes a blurbbering (four-cycling) sound. When you experience that sound, you have found the jet that causes you to run too rich. So back off one size to a smaller jet. This is the safe main jet to use. You could go another size leaner; but you need to be careful to avoid running too lean which causes the engine to run hot and could seize the piston. It's better to jet on the rich side.

Step 2: Jet Needle Clip Position and Needle Selection
The needle jet controls the mixture from 1/8 to 3/4 throttle. At the upper end of this range, the main plays a part too, but you have already selected the main jet. The slide cutaway and the needle DIAMETER are very similar in their actual effect on jetting. It's usually easier to leave the slide stock and try to get jetting to an optimum with the needle diameter. It is also possible to foul your plug if the jet needle setting causes the engine to run too rich. Raising the clip, a notch or two on most bikes will help substantially. Most bikes come from the factory jetted too rich, especially in the mid-range.
Again, you need an up-hill straight away to test the jet needle setting. This time use 1/2 throttle (it may be helpful to mark the openings) and allow the RPMs to reach the upper RPM range and leave the throttle there. Now do your listening.
Any pinging means too lean. Blurbbering means too rich. Excessive smoking is also an indication of running too rich.
To adjust to a richer mixture, take out the needle and place the clip one notch lower (nearer to the sharp end of the needle). This raises the needle out of the main jet a little higher, thus allowing more gas/oil mix to pass.
To adjust to a leaner mixture, take out the needle and place the clip one notch higher (further away from to the sharp end of the needle). This drops the needle to restrict the gas/oil mixture from flowing through the main jet.
Be careful when you remove the clip. It can flick away and become lost quite easily. I use a small flat screwdriver or a pair of needle-nose pliers and pry the clip away from the needle. I hold the needle and clip between my thumb and finger while I do this.
If you find that you are up at the top notch of the needle (there are usually 5 notches) you should get a needle with the next lower number (leaner) and place the clip in the center notch to give the equivalent mixture as the richer needle with the clip at the top. Similarly, if you find that you are up at the bottom notch of the needle you should get a needle with the next higher number (richer) and place the clip in the center notch to give the equivalent mixture as the leaner needle with the clip at the bottom.
You should not have to go to any more than one size leaner needle than stock. In addition, I would not expect you to need to go richer than the stock needle.
Next, go along slowly in one of the lower gears at less than 1/8 throttle and move the throttle quickly to 1/2 throttle. If the engine does not pull strongly, it just sort of gasps for breath and only runs well after the RPMs build up, it is an indication that the needle is too lean.

Step 3: Pilot Jet Selection and Air Correction Screw Adjustment
When you are at 1/4 throttle and more, the pilot jet has virtually NO effect. The pilot jet affects cranking, idle, and particularly acceleration from idle. If the pilot is too lean, the motor will hesitate when accelerating (in neutral) off idle. If it's too rich, the motor will smoke excessively, foul plugs, and be unresponsive off idle. After you get the needle right, get the bike idling by adjusting the idle stop up where it will idle slowly on its own. The air correction screw should be at 1.5 turns out to begin with. The airscrew affects the pilot somewhat; it's about like changing the pilot 1/2 step (if that were possible). Okay, now slowly screw in the air correction screw 1/4 turn. Try to find the airscrew adjustment where you get maximum idle RPM. You may have to open the screw to 1.75 or 2.0 turns to get the right setting. As the idle RPM increases, turn down the idle stop to return the idle RPM to a slow, correct idle.
You objective is to find the pilot jet that will give you maximum idle with the airscrew set at 1.5 turns out.
Remember that opening the air correction screw admits more air during almost-closed throttle making a leaner idle mixture.
Now, when you find the correct jet size you will want to do some final air screw adjusting to improve throttle response, assuming that the needle jet is properly adjusted. Let the engine idle for 5 seconds then open the throttle abruptly and be aware of how the engine responds. If it almost dies, then you need a slightly richer idle mixture so that as that mixture is gulped at abrupt throttle openings it will be just a little rich and therefore give good response. The bottom end should be a little on the rich side, while the mid and upper end (the needle and main jet) should be leaner to give you the best throttle response.
You can test this as you ride, say slowly in 2nd gear, with the throttle closed so that the engine is drawing only from the pilot. Wick it open quickly. If you find yourself doing a wheelie, your air correction screw is set right. If instead the sound is uhhhhhhhhhwwaaaaaaa and you find your nose a few inches from your triple clamp, then your idle mixture is too lean and you need to close the screw a little.

Rich Jetting Symptoms and Solutions
A) Motor won’t idle and idle set screw is ineffective. Try leaning out the airscrew by turning it counter clockwise a quarter turn at a time. If the airscrew has no effect, install a leaner pilot jet and return the airscrew to 1 turn out. Proper airscrew settings are usually between 1 and 2 1/2 turns out. The correct pilot for your bike is one that allows instant off-idle throttle response, and allows the airscrew to be effective between 1 and 2.5 turns out. If the problem still exists, check and clean the choke circuit and carb vent lines.
If you turn your airscrew 3 turns out you would need a smaller pilot.
B) Motor stumbles off idle to 1/2 throttle, then cleans up. If everything in part A above is correct, check the needle. Stock position is usually in the middle, but check your owner’s manual to be sure. To lean out the needle, you need to raise the clip. If the needle is dropped all the way lean and problem still exists, try a leaner needle.
C. Motor will rev through the mid range then becomes gurgled (technical term) at full throttle and power is sluggish. This is a textbook example of a rich main jet. This problem often occurs when an air filter becomes clogged and gets worse as the motor heats up. Choose a main jet with a smaller number and lean out the air fuel mixture one step at a time. If the problem persists even though it’s improved a little, reinstall your original main jet and lean out the needle one position. Now fine-tune the main jet with plug checks.
Plug checks are the key to fine tuning the main jet once the other circuits are set.

White Porcelain Lean
Chocolate Mocha Brown Perfect!
Black/Wet Rich
Look for symmetrical burn patterns, smell for odors like burnt plastic, which is actually transmission fluid and would be indicative of a blown seal.
Lean Jetting Symptoms and Solutions
A) Motor hesitates off idle with a "Booooowang" sound. This is a lean symptom and often occurs when a motor is cold. Try turning the air-fuel screw clockwise a quarter turn richer and check throttle response again until motor revs without hesitation. If the motor "hangs up" or doesn’t come right back down to idle, install a richer pilot, and reset airscrew.
If you throttle on from idle and it bogs try turning the airscrew in or out a 1/4 of a turn at a time until it does not bog at all.
If it still bogs - turn it in. If you have to go in more than 1/2 or 3/4's of a turn in you'll need to put in a bigger pilot jet.
B) Motor knock knocks at idle when hot. Try solution A. If problem persists, perform a "leak down pressure test" to check for ignition crank seal leakage.
C) Motor revs clean and crisp but runs really hot and lacks power. This symptom indicates a lean main jet and/or needle. Use a richer main jet and/or needle setting. This is the most common misconception about two stroke jetting: When a motor runs excessively hot and lacks power, it is on the verge of seizing. If you are on the trail and don’t have the right main jet, try raising the needle by lowering the clip. It won’t be exact but at least you won’t seize.
Note: To be certain that your problem is lean, pull on the choke and see if the problem gets better or worse. If better, your problem is a lean condition. .........I in no way express this information as being my own.

[Suzukidave]

Some more added by another post ..... Two things I disagree with on the two instructional's posted here. In the first one, I believe it is just an error in wording, "if your bike starts easily without the choke (few two strokes actually have a true "choke", but an enriching circuit instead) it is too lean". Just the opposite is true on the starting.

In the second one, paragraph 3 states that the low speed circuit has little to no effect after 1/4 throttle: At about 1/8 to 1/4 throttle the low speed jet or circuit will be contributing as much fuel as it is going to, but it DOES NOT shutoff. As circuits are opened or exposed they stay open and or exposed until the throttle is closed past their point of actuation. As long as the throttle is open and you have vacuum (ie the motor is turning over) the circuits keep flowing fuel.

[tz375]

Some more added by another post ..... Two things I disagree with on the two instructional's posted here. In the first one, I believe it is just an error in wording, "if your bike starts easily without the choke (few two strokes actually have a true "choke", but an enriching circuit instead) it is too lean". Just the opposite is true on the starting.

In the second one, paragraph 3 states that the low speed circuit has little to no effect after 1/4 throttle: At about 1/8 to 1/4 throttle the low speed jet or circuit will be contributing as much fuel as it is going to, but it DOES NOT shutoff. As circuits are opened or exposed they stay open and or exposed until the throttle is closed past their point of actuation. As long as the throttle is open and you have vacuum (ie the motor is turning over) the circuits keep flowing fuel.

Correct Dave.
If it starts without choke, it's jetted too rich
And again. The pilot circuit continues to flow fuel even at WOT. I suspect that the writer was trying to suggest that adjusting slow speed jetting makes no discernible difference at wider throttle openings. The amount of fuel from the pilot jet at WOT is say4% of total fuel and a change of a couple of jet sizes on the pilots will be 10% of 4% and not measurable.

[Vintageman]

I don't fully agree with slide cut being equal to needle dia etc. There is definitely overlap, but my experience on sleds you could really improve small throttle cruising/off idle throttle performance. And, there is not and infinite amount of Jet needle profiles to choose. Unless your Ivan and make your own.

Suz bikes due to custom carb slide can be hard to try this option. Somewhere I found these under slide fillers. I think are more for smoothing air flow/turbulence (good idea) under slide area but could also be used to change it to a richer cut. You can always make a leaner cut with a little machining, better have spares

There were two other articles that I found in my life (wish I could find again). I'll paraphrase

#1 Throttle position and rpm should not be related. You should be able to hold any throttle position and it should would perfect from low to high rpm light/heavy load. Such an amazing tune when achieved for street riding... My goal always

#2 Quick Wick between each jet circuits. a circuit transition test. Kind of like the classic if you are at idle and crack what it does : Baaawaaa or Wheelie. Do same thing from full to 3/4 and 3/4 to full. For example if full to 3/4 is clean up and pulls harder full too rich main. When 3/4 to full no change you may be too lean WOT. I have found this to be a good butt fine tuning for sure

And, I am not afraid of lean. Not that I run lean (so me thinks... if wrong i'll fix it) I just won't choose to be too rich in fear of being too lean. MPG is a good general test for too rich on a jet circuit. Street riding tune is always a challenge since your not typically just WOT

Fun Stuff

[tz375]

And the comments about plug color are dead wrong too.. But generally a good read and good place to start.

Slide cutaway is most important at the just open to around 50% mark.

Needle jet size/needle root diameter are also most effective over more or less the same range. Needle position has an effect all the way through but is most effective slightly higher up the opening range. That said, each bike is slightly different and the effects of different circuits may be relatively bigger or smaller. And let's also remember that different motors respond differently to a lean or rich mixture. One may tolerant of a lean condition and falls on its face if rich and others are the other way round.

All that the charts show us is change in fuel flow rates relative to throttle position but none show us the third dimension of RPMs.

Mikuni carbs tend to track well from one circuit to another and it's really easy to get one setting wrong and then over compensate on an overlapping circuit and chase your tail trying to eliminate a flat spot caused by an earlier decision.

With VM Mikunis on Honda twins it's easy to get them rich at idle, massively lean as throttle is opened going to way rich a poofteenth later and so on.

Ivan has a much better handle on this and on how different bikes and different versions of similar carbs work. All of us can get idle jetting right and WOT right and yet we ride in teh 1/4 to 1/2 range most of the time and that's easiest to get wrong

And Thanks again Dave for posting that info.

[Vintageman]

I think in general a carburetor's body pulling pressure (Bernoulli) is based on the square of velocity, but a jet limits flow more based on viscosity which is more proportional to pressure. So these two don't change one to one and over an infinite range can be far out of tune. Importantly, these carbs are designed to cover a wide usable range of RPM pretty well at fix throttle me thinks.

This test (fix throttle-wide useable rpm) will show how well "centered" a circuit is tuned. And, why I preach so much about the inside of the needle jet being shinny smooth .

[tz375]

Yes, and air and fuel have different SG so their flow changes relative to each other as speed increases just to complicate things.

In general that's a second order effect, but that's what's at play on full throttle as engine speed increases - the mixture changes.

And of course that's where EFI is so much easier to adjust as long as it's close to begin with. Carbs are so simple in basic principle and all those compensating techniques like air jet sizes, and the size of the air holes in the air bleed and height of the spray tube all have been optimized at the factory to get that wide throttle range that you are talking about.

The rest of us are happy if we get our bike to run half way right after we modify it. Most of us are not so good at the D part of R&D. That's where we have to appreciate the huge amount of work and experience that guys like Ivan bring to their craft.

[Suzukidave]

Thanx guys for adding your knowledge to this topic

[Vintageman]

This Kawasaki stuff is good too, A lot of people fooled with them
http://kawtriple.com/mraxl/carb/carbadj.htm" onclick="window.open(this.href);return false;. Near the end they are take about using J&B Weld to richen/build-up a round slide cut if too lean. This stuff for engines better than Duck Tape.

You may have seen this elsewhere but shows slide cut affect ->
http://www.howtomotorcyclerepair.com/ho ... e-cutaway/" onclick="window.open(this.href);return false;

Limited number of slide stuffers -> http://www.hiperf.com/acatalog/UFO_Carb ... fers_.html" onclick="window.open(this.href);return false;.

Sleds forums love these things

One thing I like about riding two stroke more than four. Four stroke to get more RPM you have to give more throttle. it seams kind of 1 to 1. Two stroke you just easy throttle and engine will climb rpms if not loaded too heavy. probally a lot of factors here but, man for me that lazy (too lazy to twist throttle once set) agressive (let it climbs up in RPM before next shift) street riding is enjoyable.... I think what a lot of people mean by "so smooth".

Fun stuff