User's Manual

1-10 GENERAL INFORMATION
Technical Information – Air Inlet System
Subthrottle Control System
The ZR750–J1 employs large bore throttle bodies to increase power output. However, sudden
changes in throttle opening can cause hesitation and jerky throttle response with a single butterfly
valve in a large bore. Therefore two throttle valves are placed in each inlet tract, the main throttle
valve located closest to the cylinder and a subthrottle valve placed further up the inlet tract. The main
throttle valve is operated by the rider when the throttle grip is turned clockwise or counterclockwise,
while the subthrottle valve is operated by a stepping motor controlled by t he ECU. The subthrottle
valve automatically adjusts air inlet to m ore precisely match engine demand, so that when the main
throttle is opened quickly there is no hesitation or jerky response.
The subthrottle valves allow the fuel injection system to provide smooth throttle response, similar to
that of a constant velocity carburetor, no matter how quickly the throttle is opened.
A. Main Throttle Valve
B. Subthrottle Valve
C. Throttle Valve
D. Vacuum Piston
E. Inlet Air