One possiblity is air lock. Try turning it on, putting motor in reverse and goosing a little bit. The pressure will help prime it and it'll work from then on. My G3 used to do that sometimes.

If air lock is the issue, reseating the hoses usually will help.

Have you visually inpected the impeller? Lot of times, the impeller will crack and it'll spin on the shaft or the shaft will get line on it and slow it down enough so it can't prime too.

Other than that, and inpsecting for blockage in the hose, replace it.

Wannabe...