It's about spark plug color. I live at 5,000ft above sea level. Just got a genuine dellorto 16.16. To make my motor run good, I put in a .58 dellorto jet. This made the motor run real nice, just a tiny tiny bit of 4-stroking at very little throttle, but other than that smooth sailing. Attached are photos of my spark plug (B6HS) next to a brand new plug after a 10 mile ride, no plug chop just regular riding at about half throttle for the most part. Before I switched to the B6HS, I went on a 20 mile ride using a B8HS and a .62 jet. The .62 jet made the engine 4 stroke up until about half throttle. When I checked the plug after that ride, the plug looked pretty much the same as the pictures below which confuses me. I love how my motor is running now, but I am scared that my motor is running too lean based on the pics. Please let me know what you think. Spark plug on left is the plug I'm concerned with, the one on the right is just a new one for comparison. I believe the last photo the plug looks a bit darker than it is due to lighting, but the first 3 look pretty accurate.