What is the ideal squish clearance for a latest-generation engine YZ250 used off-road? I've done some extensive web searching and this forum is the only place with people who seem to know anything about it. I asked the same question of my CR250 on another forum and only heard crickets chirping. It seems like RCannon may have come across the magic number here. I just picked up a 2006 YZ250. It rained that night so of course I had to ride it the next day, sans spark arrestor. The only mods were tires/tubes and some more grease in the lower linkage bearing. I burned less than a tank of VP C12 (with a more generous ratio of Motul 800 for break-in) and didn't change anything but the suspension compression. Tonight I took the head off and measured the squish clearance at .071", 1.8mm. Wow, that's a lot! With a Cometic high-compression gasket kit, my CR250 measured .057"/1.45mm, which still might be too much. I plan to have a machine shop take some material from the head to get to my ideal squish clearance. I am aware this will lower the volume of the combustion chamber, but that, too, is desirable. I ride at 4,500-7,000 feet and I use pure race fuel or a mix of race/pump gas. (There's actually a VP gas station nearby, how cool is that?!) I'm learning a lot about two-stroke tuning because I bought a TZ250 roadracer this summer. That requires careful attention to deck height, chamber volume, squish clearance, ignition timing, etc. I had a hard time getting clean, consistent carburetion from my CR250 with its Mikuni, but now I'm wondering if excessive squish clearance was the major contributor to those difficulties. (I did manage to get it perfect with a Keihin carb.) The first ride on my YZ showed no major carburetion issues. But before I go swapping brass, I want to get the squish clearance right. So what's the magic number for a YZ250?