My take:
Surging: At a steady throttle, light engine load, the engine speed varies a small amount which feels like the throttle is being opened and closed a tiny amount even though it is being held steady.
Abrupt power delivery: When the throttle is closed the engine goes into a decel FI routine where fuel injection is basically turned off, then when power is asked for again there may be small hesitation without response as the throttle is rolled on, then suddenly you get all the throttle that you dialed up.
Abrupt Throttle Response II: The Gen II throttle cam is eccentric (not round) causing the throttle to respond in greater proportion than what the operator intended. The steep ramp of the throttle cam is right around the 3k rpm range. A second issue are the gorilla springs on the throttle pulley making fine throttle control difficult and tiring. A G2 throttle tube & cam will neutralize the eccentric throttle cam. Some people acknowledge the risks and partially unwind the throttle springs to lighten up response.
Drive line lash: Free play between the engine output shaft and the rear wheel. With the bike on the center stand, engine off, in gear, rotate the rear wheel and note how much free rotation it has. This could possibly cause the same feel as abrupt power delivery and/or surging.
Altitude sickness: Total lack of throttle response, bogging, very poor drivability. Often initiated by rapid altitude change, often reset back to normal operation by cycling the key off/on. This is covered by an ECU recall by Yamaha.
Buzz: Rapid mechanical vibrations, usually felt in the bars and pegs first and as it gets stronger the frame & tank. There is a common rpm range someplace between 4k rpm and 6k rpm. It is not unusual for some bikes to buzz at one rpm and another bike at a different rpm but the buzz is almost always in a range that you can pass through and get smooth operation again.
Buzz can usually be all but eliminated with a good throttle body sync (TBS). There are a lot of other tweaks, like fuel management via a Power Commander III that can be done to help too. Sometimes loosening the engine mounting bolts and retightening will get stubborn buzz to quit. Don’t do the engine bolts without the service manual’s specific order. Bar end weights and Grip Puppies are a way to manage residual buzz.
