Yes you need to use it when ever you come to a stop, you probable need to also adjust your clutch some. There are threads all over about it but if you need some more help just ask. If engaging the clutch is a problem then you can always get an auto clutch. (centrifugal) In regards to the carb leaking you might try tightening it up and if that isn't working tearing it down and rebuilding (maybe a new float and that kind of thing). Also the petcock you have is probable worth sh*t. (assuming you have the ones that you get from the kits.) Mine have never leaked but I hear it is a problem. You can get a replacement one that is much better from SBP.
Keep asking questions the more I talk the more it looks like I know