"it has to go through the carb to come out of the exhaust"
...new one on me!!
You have more than likely tipped it on its side recently to probably clean it underneath. If you have, then the engine oil has slowly migrated from the sump and into the exhaust. It you start it up and leave it running for a few minutes the excess oil will be burnt of and the white smoke will clear.
pleasant, May 2010
