Having replaced the engine I was thinking about how to ensure fuel was getting down to the pump. Not having a spare fuel cap to hand (although I think this would be the better way) I rigged up this Heath Robinson device which also does the trick. It is a section of a 2.5" motorcycle inner tube (think Honda 90) with one end folded over and glued and the other end stretched over the filler cap. Attach a bicycle pump and it does put some pressure into the tank. A large diameter hose clamp around the inner tube/ filler interface would allow higher pressures.