It?s happened twice. Once during the PAP while conducting the ?time to climb? performance test, and once during the first flight I had a totally full fuel tank. I had read all the posts on probable causes and I went looking for the obvious. While removing the access panel to check the tank/fuel line tank fittings, I noticed, thanks to a liberal coating of exhaust products on the bottom of the airplane, that the tank had been venting significantly, at least during the second occurrence. As I followed the flow path aft, it was pretty clear the vented fuel was entering the fiberglass tall cone at the attachment. It does overlap the aluminum skin at this point. And btw, there was some traces of fuel on the trailing edge of the trim tabs. My conclusion was that it pooled in there then the fumes migrated forward through the tail cone to the cockpit.
I checked all the fittings and inspected the carbs anyway, but for those of you chasing sources of intermittent fuel fumes in the cockpit, you might want to consider this possibility as well as looking for a leak.
I checked all the fittings and inspected the carbs anyway, but for those of you chasing sources of intermittent fuel fumes in the cockpit, you might want to consider this possibility as well as looking for a leak.