This is pretty funny to me since just earlier this week I experienced this for the first time. I have a plastic gas tank and was trying to get back to the dock before the sun set, and the engine started puttering out and getting hot. We decided to stop the motor and try throwing the sails back up, but the wind had died. The motor cooled off and I pulled on the cord and started heading back again, just to witness the same heat and missing. I looked at the tank and thought, "what the hay, it can't hurt..." so I opened up the vent and wha-lah, ran smooth again. I figured I had never had that problem before because it usually is running while in the sun, and the sun was starting to go down and it was cooling off, instead and creating a vacuum. Lesson learned - also, don't forget to close it back up before you pull the boat out of the water if it's a portable plastic tank... It could flop over and spill gasoline (didn't happen to me, but it could have if I hadn't remembered to close the vent). Alex M15 #281 Portland, OR <<<<< first thing I would try is to open your gas cap and see if air rushes in or if it improves your motor's performance.>>>>