Actually, I noticed the carbon on both the nut and the threads when I open up the outside cover after 10 flights to re-tighten the header. The carbon coated the inside of the nut so badly to the point I couldn't even fit the hex key for tightening. I had to scrape off the carbon with an x-acto knife before I could insert the hex key into the nut. I hope this is just an isolated case, I sure hate to keep sending engines to YS. May be I should really look into electric, nah, just kidding.