blocked fuel tank vents-lesson learned
 

Recently when removing left fuel cap for pre-flight, fuel gushed out and I had to replace the cap to stop the flow. both tanks were filled at he same time and on a level ramp. The next pre-flight, both tanks showed half full. This time when I removed the cap on the left tank, there was a loud sucking vacuum noise. Lucky for me, the mechanic was close by. He immed. diagnosed the issue as a blocked fuel vent and cleared it. he also found the fuel cap vent was cloged and had to replace The consequences of furthed flying with this issue are well known-I had already experenced some surging of the rear engine when in cruise. Hope this helps someone.
Dick

Just talked to mechanic--to fix, he removed wing tip,disconnected vent line at check valve, blew out vent tube. He said no vacuum could develop in tank due to check valve and vented filler cap, which was junk.