Dunnit as well!
Beagle Pup has the fuel cock on the floor in front of the seat squab. Tapered pointy thing on top. Point it in the direction of the tank you want or forward for both, rearward for off. Needless to say I'd switched form "Left" to "Both" but had ended up with it pointing backwards rather than forwards.
One of the reasons not to change tanks near the ground or immediately before take-off or landing.
