<![CDATA[The objective of this research are to investigate: (1) the effect of variation of Groundstrap wire diameter on the torque and power of Yamaha Jupiter-Z motorcycle 2007; (2) the effect of variation of ignition timing on the torque and power of Yahama Jupiter-Z motorcycle 2007; and (3) the effect of interaction between the variation of groundstrap wire diameter and variation of ignition timing on the torque and power of Yamaha Jupiter-Z motorcycle 2007. This research used the descriptive quantitative method. The sample of the research was Yamaha Jupiter-Z motorcycle 2007 with the engine serial number of 2P2675042. The research was conducted at Mototech Motocourse Technology, South Ringroadstreet , Bantul, Jogjakarta. The data of the research were obtained through documentation of the result of measurement of torque and power resulting from print out research tool Sportdyno V.3.3. that based from research groundstrap installation (with diameter of 0.25 mm and 0.40 mm), ignition timing (13° BTDC and 7° BTDC) and interaction of the groundstrap installation and the change of ignition timing. The results of the research are as follows: 1) The maximum torque of the standard condition test is 8.59 Nm, and the maximum power is 8.30 HP. The test with the groundstrap installation with the coil wire diameter of 0.25 mm results in the maximum power of 8.33 HP and the maximum torque of 8.89 Nm. Meanwhile, the groundstrap installation with the coil wire diameter of 0.40 mm results in the maximum torque of 8.89 Nm and the maximum power of 8.37 HP. 2) The test of the ignition timing of 7° BTDC results in the maximum torque of 8.89 Nm and the maximum power of 8.33 HP. Meanwhile, the test of ignition timing of 13° BTDC results in the maximum torque of 8.78 Nm and the maximum power of 8.50 HP. 3) The results of the test indicate that the highest maximum torque and power are obtained from the interaction of the treatment of ignition timing of 7° BTDC and the groundstrap installation with the coil wire diameter of 0.25 mm. The torque and power produced are 9.05 Nm and 8.57 HP respectively. 4) At 4500 rpm of the engine speed, the result of the research showed increase with more clear. Based on research, the result of the torque research at 4500 rpm showed the increase between 27% to 47%. The result of the power research showed the increase between 24% to 44%.]]>
