I have a 99 YZ 125 that I think may need crank seals. I've checked the carb, reeds, cylinder torque, head torque. The plug is super lean. I went to a bigger main jet and raised the needle and it was still lean. I run Amsoil Series 2000 @ 36:1 with 50/50, 94 pump/110 race fuel. The bike starts perfect, will sit at idle, rev with the motor under no load and it sounds fine. When I drop it into gear and give it throttle the motor cuts out violently. I can lug it or run at WFO and it runs good, but when I try to accelerate from the bottom end it's not good! I don't have a leak down tester so I'm hoping someone may know what's up.