I start my tractor up and its ok after it runs for a bit white smoke comes pouring out. Any ideas what it could be?

Hopefully somebody can help us. Now I have a bigger problem, I was mowing the mower just shut down, I thought it was because it was out of gas, It was low on Gas. But I filled it up and went to start but their is nothing their completely dead, I plugged up the jumper box and checked the battery but nothing I did pull out the regulator and tried touching the starter and it wanted to. Dont want to buy a new regulator unless I know for sure thas the issue.
Please Help.