Ok now I'm not saying that this is everyones problem but nine times out of ten, if your Bug is running good when your on the gas but when you come to a stop it stalls, this is what the problem may be. Is what happens is that the Pilot jet gets something in it, like dust or gas drys in it and clogs it. It dosn't take much. All you have to do is take it out and blow it out with an air hose or something that has alot of psi. DO NOT PUT SOMETHING IN IT TO CLEAN IT OUT IT MAY MAKE MATTERS WORSE. If you don't know where the Pilot jet is, here is a few diagrams of the stock carbs to show where you can find the pilot jet and what thay look like.
SOLEX 34 Pict-3 SOLEX 30 Pict-3 SOLEX 30 PICT-2 SOLEX 28 PICT 30 PICT-2