At a loss and so is the dealer. 89 Gl1500 on accassions will start and when the fuel bowl is empy (about 1 block) it stops as if out of gas. Towed to dealer - they prime it or tweak and it is fine for a few weeks then again it happens. they have replaced vacume lines, shutoff devise (sorry for my technical ignorance - silver round valve by gas cap). They say seems to have strong vacume, fuel pump pumping great, but no idea why this keeps happeing. 6 times in 6 months. Any ideas?