I was recently having a problem with what felt like my clutch. Specifically, while in gear cruising at 6 or 7k rmps when i went to punch to pass a car etc... the motor would tach up to about 12 or 13k rpm. A friend said sounds like the clutch is slipping. I then took it to a large reputable dealer in South NJ. A mechanic asked me what kind of oil i was running. I told hiim Full synthetic Mobil 1 motor oil, not the motorcycle Mobi 1. He said that was my problem, that I CAN NOT run full sythetic oil in my k4 600. He said the oil is too slippery and causes the clutch to slip and become damaged. I never heard of not being able to run full synthetic. After reading all of these posts that alot of guys are running synthetic, i can't believe that i never heard of this. Anyone with any info??????