I have a 99 YZ400F. Adjusted the valves maybe August of last year. they were very tight then. Checked them 2 days ago in anticipation of spring. Found the following: Exhaust clearances are .13 with a 145 shim in it and .10 with a 140. Intake are .13 with a 145, .12 with a 155 and .12 with a 145. Obviously very tight. How many more adjustments do you think I can get if any? Is it time for a new head? Any other options?