Start by cleaning and disassembleing the carb. Replace any broken or worn parts in it. If it still pours white smoke and there is fuel in the oil, try putting a fuel additive in the oil such as Sea-Foam (avalible at most hardware stores) If it still isn't fixed, you might have serious problems, such as broken rings, scored cylynder walls or a cracked piston. But don't panic! With some simple tools (wrenches, socket set, torqe wrench, screwdrivers etc.) you can install new piston and rings. However, if the cylender wall are scored, you have better start looking for a new engine. There are lots of these around, try looking on craigslist or ebay. Or, if you are good with fixing things, you can browse in a scrapyard for a old one. Then you can use parts off your current one to repair the one you got from the scrapyard. All these latter ideas (except the scrapyard) will probably cost around $100. Hope this helps!
SD redneck :), October 2012