Sputtering fuel update

Just in case anyone comes across this again: Some time back I mentioned that I would get a sputtering problem as if there was water in the fuel and when I switched over to reserve it would go away. I appreciate the many, many replies. However no one hit on the right remedy. I recently had a new tank painted because the original had two bad front dents. When I removed the petcock from the old tank, I noticed that the small rubber ring that slips over the fill tube had come off and was floating up and down inside the upper part of the screen. Evidently it would get sucked down on top the fill tube and when I switched to reserve it would loose suction and bounce around for a bit until it got sucked down again.
All of this is the result of my changing the diaphragm in the petcock about 3 months prior. The screen didnt slide out when I changed it and re-insertion of the fuel tube pushed the rubber ring up and out of position.
So for inquiring minds that want to know. There ya go.