Was out riding yesterday when I bumped a stump and the engine hit WFO with no control from the handle. Shut it down and found that the linkage rod from the govenor arm to the carb had come loose at the carb. It can't come loose at the govenor arm due to the "S" bend at the connection. But at the carb connection it is just a 90 into a hole. It is held in place by tension from a plastic grommet in the hole. The plastic grommet wore out on mine allowing the linkage rod to just fall out. Your throttle will hit WFO when it happens in the Verticle setup over-reving the engine. Needless to say it ended my run early. I found this product at Lowes to fix the issue, Hillman brand 3/32" Flat Fast Nut. Would not hurt to buy some and put one on before hand to prevent this from possibly happening to you. Cost about .50 or so cents for a package of 4. Just press over the rod ends.
http://www.lowes.com/lowes/lkn?action=p ... 8&lpage=no

I ate up one of the plastic bushings and harvested one off an unused hole in the throttle plate on the back of the motor. Good idea especially if the vertical accellerates if it disconnects.