Sounds like he's running into resistance during the throw where the shift fork is moving the gears. I'd follow Typhoon's advice and attempt a cable adjustment (which is free and easy) before delving into other possible causes and solutions.
Here is the complete procedure per the service manual. Note that to access the shift cables you will need to remove the section of induction pipe that connects the air box to the crossover pipe.
Also, DO NOT unclip the shift cable clip with a tool, and DO NOT remove it completely! USE YOUR FINGERS to release the tabs on the top and bottom. It can be very delicate and if you break it you will need to either bodge together a fix with zip-ties or buy an entirely new shift cable, as the clips are not available by themselves.
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