I have a Troy-bilt self-propelled mower model 830, I've had it less than a year, but now it want pull when the lever is down for the self propel, what could be my problem?

Check to be sure the belt is not loose or broken. You can adjust that handle to pull more cable, it may have slipped.

Hi,
Another unusual problem that surfaces with MTD-made machines that are variable speed is that the system can jam. You may try holding down the bail and moving the speed control from minimum to maximum a couple of times. There should indeed be a thumbwheel to adjust the cable.
Peace,
Clarke