[davepl]

For a bigger leak carb cleaner or a propane torch will help you - you can just turn the torch on (not lit of course) and let the propane flow to the carb base and so on. Or spray the carb cleaner around the base. Don't forget to turn the torch back off when done...

In either case if there's a substantial leak it'll pull that combustible material in and the idle speed will change, or you'll hear the engine respond at least.

But if it ran OK when parked, I doubt it developed a vacuum leak in the interim. More likely to be junk in your carb somewhere. It doesn't necessarily need a "rebuild" with all new parts but it'll likely need to come apart for a good cleaning.