Hi vti-chris, I had exactly the same thing on one of my 5 Ports which has about 2.5 gallons through it. When I pulled the carb I found that the bottom carb O ring (the brown coloured one in the crankcase housing, not on the carb neck itself) was all shredded. I couldn't get another one at the time so cleaned it up as best I could and reinstalled the carb with some new silicone. Motor runs fine and doesn't have any leaks in this area, but the carb still moves slightly left and right when throttle applied. I am only running one silicone throttle return band and linkages are all good, so the O ring would appear to be the problem. It is worn just enough to allow the base of the carb some slight sideways movement. Replacing the lower O ring should solve the problem. My other 5 Port is fine. I think someone else had a similar problem a few pages back.