As with most carburetor problems, there can be more than one reason for this.
I have to ask the question: Does the engine idle OK. If not, then look at these things:
- Electrical system not up to par
- Vacuum leak
- Idle mixture
- Clogged idle vent passage
Otherwise:With most carburetors this problem can be caused by a warped carburetor, or possibly the wrong float bowl gasket. A warped carburetor can allow gas to splash over into the bore from the float bowl, thus making the fuel too rich. If this problem occurs around corners also, then my bet is on the warped carburetor.