Thanks, my test was with 2 short lengths of neoprene tube attached to the fuel tap into a container. Tubes hanging vertical. However, there was less than 5L fuel in the tank. The bike took an absolute age to fire up last week and then lacked power. Now that the tank is drained I will try blowing up each pipe with the other blocked and the fuel tap still fitted to the tank. I`ll also take a look at the fuel tap filter. Perhaps I should keep the tank full to aid gravity feed.