On my son's XR100 ,and his older XL75 there are marks on the flywheel, an F and a T. I believe the T is TDC, and the F is a few degrees BTDC where the engine fires. I have always set the valves on his .008 exhaust and .006 intake. Actually that is where I use to set my old XR200 also. I found any tighter than that, especially exhaust, and it wouldn't start when hot.