I likely have thousands of hours on my 07 yz450f and it wont kick start anymore. Maybe it will start if I kick it for 30 mins plus. However, it runs once bump started, and will restart once warmed up. it does feel tired with low compression. Today, I measured the valves at top dead center as per manual, the exhuast valves are both at .20mm and I cant even get a feeler into any of the intakes. I have a new timing chain coming Monday, was thinking maybe it stretched a tad and for preventative.