Take your float off and shake it next to your ear -- hear any sloshing?
Fuel inside the float can give you the symptom you write about.If you float is soldered brass.To get it all out, heat it in a mild 200 degree oven for a half an hour.
Now chill it in the freezer for 15 minutes then briefly immerse in warm water for no more than 5 seconds. String of bubbles from expanding cold air should mark your leak location. Mark spot for soldering repairs and wipe all water off the float.
After fixing, repeat the steps to check for any other leak location.
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If you are blessed with a plastic float, do the freezer steps to spot the leak. Put the plastic float out on the hood of your car for a day to see if you can get the liquid out from inside it, then use plastic glue to patch the leak location.
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If you have no fuel inside your float, then your vac petcock is acting up on you and is simply trying to drive you nuts.
http://suzukisavage.com/cgi-bin/YaBB.pl?num=1251932429/1This, unfortunately is far far more likely than a leaky float .....