The 225dx that I had was godawful noisy, and the valves were set, timing chain set, everything, and it had no top end trouble. I never figured out what it was. But yes, service manual will be your friend.
This is my trike. There are many like it but this one is mine. My trike is my best friend, and it is my life. I must master it as I must master myself. My trike without me is useless. Without my trike, I am useless. I must ride my trike true. My trike and I know that what counts is not the amount of miles we ride, but the time we ride together. My trike is human in it's own ways, therefore I will learn it as my brother. I will learn it's weaknesses, it's strengths, it's parts, and it's soul.