the results are in -- the check valve alone did not solve the problem. when getting gas the other day, i got the "soda can" hissing sound mentioned by mudkicker and rohnk. it was not present before the return line was re-instated...
which leads me to believe i have a multi-part problem...previously, i think the tank was venting thru the return line somehow, but there was still too much pressure which flooded the carb. now, the return line doesn't allow this which gives the excess pressure at the cap. is this due to the cap not venting properly?