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?