i am in sw florida, at sea level, i thought the pilot jet is for idle and needle is for lean and rich. i have it the needle in middle ,
No, they are for tuning different parts of the throttle circuit. Here is an excerpt from an article on PSTuning. Link-----
http://forums.pstuning.com/index.php?act=home
…..Please remember that we tune each of the carburetor circuits based on throttle position and not RPM. We also go from the bottom to the top, because to varying degrees there is a culmination/overlap of mixtures from one circuit/position to the next one. If these overlaps were not present and correctly tuned for… you would experience flat spots or bogs and/or surges as you open the throttle.
Idle to about ¼ throttle opening is primarily controlled by the pilot circuit and this fuel/airflow continues all the way to WOT… and thus affects the whole jetting spectrum. This is one of the major reasons that you jet from the bottom to the top.
1/8 to about 3/8 is controlled by the slide valve cut away.
¼ to about ¾ is controlled by the needle jet and jet needle.
5/8 to WOT is controlled by the main jet.
Note how each circuit overlaps!
An important point to note is that if a particular circuit is either too rich or too lean… the amount of overlap can shift up/down, shrink/expand the range that it should normally control. Due to an engines design characteristics, rider driving technique and a multitude of other variables… a particular circuit may need to be richer/leaner than it would be in a different situation. Then an adjustment would have to be made on either side to make the transition smooth.
The transition from one area to the next doesn't have a Red or Green light…it has a blinking yellow, and just like in driving, you need to proceed with caution. If you start from the bottom and go up… you’re tuning for these variables as you open the throttle… allowing the next step to be more defined. Remember… that’s what we’re looking for… smooth transition from bottom to top, with the correct mixture ratio. Then as you roll off the throttle you'll have a smooth transition back down the range also. This is just as important! A lot of two stroke engines start to seize shortly after you come out of the throttle, not when you are WOT! Why… because when you shut off the gas, you also shut off the oil, and after a long WOT run you have built up a lot of heat, and you need the gas/oil mixture to protect your piston/cylinder walls.
Now that we have the float level set and have a basic understanding of how the circuits affect each other… let’s just do it!
The pilot circuit is controlled by the pilot jet and air/fuel adjusting screw. If the adjustment screw is on the engine side of the slide it controls the fuel, and if it’s on the air cleaner side it controls the air. Most MX style carburetors have the adjusting screw on the air cleaner side, so it controls the airflow. A simple way to look at this circuit is the pilot jet controls the fuel and the air adjusting screw allows you to add the appropriate amount of air to get the proper air/fuel mixture.
To tune the pilot circuit… lightly seat the adjusting screw by turning it clockwise till it just touches the seat. Don’t tighten it too snug or you might damage the seat or the taper on the end of the adjusting screw. Now back it out to a base line setting of 1-½ turns. Warm up the engine to a normal operating temperature. Adjust the idle speed adjusting screw so that you are about 500 RPM higher than your normal idle speed. Make a mental note of the air adjusting screws location, and slowly turn the adjustment screw in, and then turn it out in 1/8-turn increments, until you have found the highest idle RPM. Go slowly and let the RPM stabilize. Go back and forth a couple of times so that you get it spot on. If the circuit is adjusted properly you will have a smooth idle and the transition from idle to about ¼ throttle will be also be smooth, with no hesitations or flat spots.
Note how many turns it took on the adjusting screw to get your best idle speed. If you had to turn the screw more than one turn out from the baseline of 1½ turns, then the pilot jet is too large and you need to go down one size on the pilot jet. Now go back through the adjustment procedure again to get the adjustment screw back to the base line setting of around 1½ turns out, when you have the best idle. Most adjustment screws have a taper that works best between 1/2 to 2 1/2 turns. Using this method allows you to make minor air adjustments to compensate for small changes in weather conditions at the track and still be in the working range of the air screw taper and spring.
The next rung up the ladder is the throttle side cut away, which controls the amount of air allowed to flow through the carb at throttle opening in the 1/8th to ½ throttle range with the most affect in the 1/8th to ¼ range. Typically… slide adjustment are not required, but… you might run in to a situation where you need to change to a leaner or richer cut away. The higher the number of the slide the more air it will flow within it’s operational range. Slides are numbered in millimeters of cut away at the closed throttle position. A number 6 slide has a 6 MM cut away and a richer number 5 has a 5 MM cut away. While you can typically adjust the pilot and slide with the engine running and the vehicle still… a good on the track test is also recommended. Accelerate out of a slow, first gear corner to give it a good test. The slide works in close conjunction with the pilot circuit to allow you to transition to the next tunable area, which is the jet needle and needle jet.
We want a smooth transition from the throttle slide to the main jet. This transition is controlled by the needle jet and jet needle. When completed, we want the jet needle’s (more commonly called the needle) clip to be in the middle position, if possible, for our base line setup.
The needle is tapered, and has groves cut in one end, to hold a clip. This clip allows you to change the length of the needle. There are also small, thin spacers available, that will let you set the needle length even more precisely, by placing them under the clip.
The needles length, diameter and taper, in conjunction with the needle jet control the rate of fuel flow in each position of the needle from a little less than ½ throttle to a little more than ¾ throttle.
Needle jets come in a couple of different styles and of course numerous jet sizes. The provide additional avenue to fine tune your mid range. Some tuners find it more convenient to replace the needle jet with one size richer instead of raising the needle. This way you don’t have to take the top off and mess the springs, etc. This way your needle will stay in middle clip setting all the time. Different strokes for different folks!
Keihin and Mikuni use a different system for numbering their needles and you need to become familiar with whichever carb you are running. Give Sudco’s web site a hit and look through their needle info to find out what might fit your particular situation. You can get the mid range perfect if you take your time and have a selection of needles and needle jets, which by the way, is sometimes called an emulsion tube. Sudco also sell a tuning manual for Mikuni that it great… for about $12……..
There is more to this article and I have posted it in its entirety on the forum. I hope that this helps. I:I
