Another thing, Mr Lunger
In case your low speed mixture screw still has the metal plug covering it, use a very sharp non self tapping drywall (sheetrock?) screw and very SLOWLY penetrate the plug, right in the center... at some point as you screw it in, the plug will rotate. Grab the screw with a pair of pliers and rotate the screw as you gently pull it out. Don't spin the screw in too fast or hard,lest you damage the screw face. The screw should survive this procedure intact and can now be adjusted with a small straight screwdriver.
Do not remove or turn the screw, but squirt some penetrating oil or WD 40 into the recess and then GENTLY screw it in until it ....again...GENTLY touches the seat. Note how many turns or half turns it took to reach seat contact, and write it down for your future tuning references. You can then turn it in or out to lean or richen up the mixture and always know the factory setting.
Keep in mind that the low speed mixture circuit DOES NOT shut down at higher RPMs, but adds to the primary and secondary main jet circuits. Be aware that if you do remove the screw for cleaning purposes, it is sealed by a very small and important o ring that seats against the smooth sharp ended section of the screw. Do not lose that o ring, which is contained by a very small metal ring. These are very small but vitally important parts and if you lose them your low speed running will be sloppy and hard to dial in. The end of the mixture screw is very sharp and delicate, and easily overtorqued and damaged, so be gentle and careful. The tiny metal ring that seats against the jet and the o ring is the piece that the spring contacts. It prevents the little o ring from being chewed up, and compresses the o ring against the jet and carb body for correct sealing... very important for good tuning. Good luck. Be slow and deliberate and patient and you will succeed.
Onward and upward. Jim
PS. Your secondary main jet can probably remain stock and be OK.
To allow your secondary main circuit to come in a little earlier, you can cut one inch from the secondary spring located above the slide. I have had success with this moderate modification for years, and it makes the circuit transition a little stronger at lower RPMs and adds a bit of torque off the bottom. Do not remove more than one inch, and do not pull on the spring to stretch it. OK?
PS2. Needle profiles and main nozzles can be played with and changed around, as well as float levels...raising the float level will richen your mixture throughout the RPM range, and a narrower needle will admit more fuel...the taper of the needle determining at what throttle opening the change in mixture will occur. Many books have been written about carb tuning, but I think you have enough to work with here, and I don't want to avalanche you with too much too fast. Ok Buddy, good luck. I love my XT600e, and will keep it forever. Good choice.
