Depending on the millage on the engine, you may have loaded up combustion chambers which will cause detonation and vibration. The simplest thing to do is to use some combustion chamber cleaner straight into the cylinders like I have done when the bike did not feel right. Than use it once a month to keep the chambers clean. I would use it 3-4 times in a row at the beginning and see what happens. It will only cost you less than $10 to try this first.
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