How many people on this thread and who's bikes carb has a clit?Boo it sure sounds like you are lugging the motor and it is falling on its face,in a safe area,get it to bog and fan the clutch,I highly believe you will crash!To much throttle and to high a gear or to slow of a speed and you are killing the motor!A 125 wants to get up and sing,let that baby RIP!Do not start throwing different plugs at your bike like a dart board,learn to read your plug.A bike loading up,poorly jetted,or a mechanical problem can all attribute to the same sparkplug foul.