It's been sitting outside under a cover for a few weeks. I pulled it out to start it up this afternoon. Kicked over easy & started on about the 3rd or 4th kick. It ran for about a second or two, then quit. Big puff of white smoke out the exhaust. Now it feels seized. The kick start lever won't budge and the rear wheel is locked up when I put it in gear. It shifts gears easy. Plenty of oil in the oil tank. Top end has about 350 miles on it since I rebuilt it. Any suggestions on where to start troubleshooting? Thanks.