Moped Army

When I let the moped sit over winter and then start it again in the spring it starts hard & smokes like crazy. It seems like oil has seeped down from the oil tank into the carb bowl. Is there a check valve that should stop this. I've been unscrewing the carb bowl drain and let it flush out the oil and get fresh gas into the carb and then it starts 1-2 kicks. It seems gravity lets the oil seep down into the carb bowl if it sits 2-3 months. Thanks for any info , Rob in Walla Walla, WA