I am not able to control the speed on my troy-bilt 675 series self propelled mower. Model 12aj836e011. What part do I need to change to fix this?

Hi,
The manual covers adjustment of the speed control on pages 14-15. There is also a parts breakdown listing the cable if needed. The directions instruct you to not move the control unless the engine is running as well. The manual is at:
http://www.troybilt.com/webapp/wcs/stores/servlet/OperatorManualDisclaimerView?storeId=10001&catalogId=14102&langId=-1&pdfLink=http%3a%2f%2fmanuals.mtdproducts.com%2fmtd %2fGetFile.do%3ffilename%3d769-03451.pdf&htmlLink=
And click the I ACCEPT button. Choose Save or Keep.
Peace,
Clarke