Iv'e had the float in mine actually fill up with gas and therfore wouldn't float. I wound up with the problem you have now.
You have changed out the float... did you remember to re-install the needle valve? If so when you pull it apart, check the rubber tip of the needle valve and make sure it looks pointed. Also check to see if it is still soft. A hard tip on the valve might not allow a good seal. Check and clean the port that the needle valve seats in. Debris or buildup could be hindering the valve from sealing.