It also allowed extremely radical high lift cams that gave a very lumpy idle when unplugged in the open position or when using a full aftermarket exhaust. Yamaha continued to use the EXUP valve system on the subsequent Yamaha YZF1000R Thunderace and Yamaha YZF-R1 motorcycles.
This passage discusses the EXUP valve system used by Yamaha motorcycles, which allowed for extreme high lift camshafts that caused a rough idle when unplugged or with an aftermarket exhaust. The system was later adopted on other Yamaha models like the YZF1000R Thunderace and YZF-R1.