I did a little checking on this machine. When was the last time the valves where adj. and it had a full tune up?
I am reading that the cam chain tensioners are common failure points on this machine, causing the valves to become out of adj. (too tight) and also causing the cam timing to be off. Both will cause the same exact problems you are discribing here. Manual recommends valve adj. every 16 hrs of riding.
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