The first thing you need to check is your float level. No fuel should run from the sight hole unless you shake the vehicle. Next, check the engine vacuum at idle. (in gear if A/T). If it is 12" or more, a 6.5" powervalve will usually be fine. Anything below 12", divide in half. For example, 9" vacuum will use a 4.5" powervalve. Another possible cause associated with performance cam shafts are exposed transfer slots. You should not see more than .025"-.030" of the transfer slot exposed past the throttle plate at idle.