1977 puch maxi (2hp) all stock Bing Carb. the carb seems to get dirty fast like just after a few days. I say the carb is dirty cuz i took it apart and just ran some wire, air, and gas through the thing and it went from not starting to running great and getting up to 30mph. There is a filter on the fuel line and the gas tank is sealed so there isn't particles in the gas tank and even if there where the filter would be more than enough to catch it. What could be the problem? any ideas would be great.