Sounds like s small pump to me. Maybe get a bigger one. Or is the pump gravity fed?

If a line has a Crack or loose clamp it won't prime. Like if a straw in a cup has a Crack in the straw. Check your lines. You may be able to presure through the caps but leave the pump off and look for fuel leaking.

I recommend what jim said. Also check the pickup's. I had a cracked one and had the same issue

Oh wow! So the pickups come out as a complete piece like that? Can they be easily replaced?  Theres enough room to get them out with the tanks in the boat?   I have all new hoses installed.  But this seems very likely.

Hacker Alert

Having absolutely, positively eliminated all other possible causes:

1) VERY PRECISELY project the location on the gunwale where the fuel suction tube would intersect the gunwale if the tube were long enough.  A long drill or piece of close-fitting tubing or pipe, inserted inside the existing suction tube, can be used to do this.  Shine a bright LED flashlight on the inside of the gunwale in order to be able to see where the drill/tube/pipe is on the OUTSIDE of the gunwale, and mark that location.
2) Drill a pilot hole in the middle of your marked location.  Stick a rod through the pilot hole to verify your hole location on the gunwale.  This is your last chance to make small adjustments in the (larger) hole location.
3) Enlarge the gunwale hole to the appropriate fuel suction tube size (3/8" or 1/2").
4) Install a Swagelok (or similar) pipe-to-tube adapter fitting in the female NPT bung on the tank.  The fitting will have to be bore all the way through for your suction tube size.
5) Use your gunwale hole and your Swagelok fitting (installed in the tank bung) as a drill guide to drill out the suction tube that is welded to the tank bung.  If your tube is welded to your tank fitting, then you don't need to do this step.
6) Insert new suction tube through hole in gunwale and swage in place ~ 1/2" off the tank bottom.  I baloney-sliced the end of my tube to ensure that I didn't put it on the bottom of the tank.

The most important thing for you to do is use your existing fuel tank bung to help you locate the hole in the gunwale, since you will need to put the suction tube in straight.

Install a large, free-flowing filter upstream of the fuel pump to capture all of the crap that you just introduced onto the tank, if you don't already have one.

Electric push fuel an manual suck fuel. If you put a small gallon tank of fuel on the floor an run a line from it to pump an its works then it might be the pickups in the tank. Wheres your water fuel sep located? Do you have a fuel pressure gauge to ck the flow on pump? Could be a weakened/failing pump.

I chased a fuel delivery problem from one of my tanks for two years before I finally gave up and installed a mechanical pump with a remote-operated selector valve this year.

This was on a system that had functioned perfectly for over 20 years.  The fuel system was totally "against the book": A high-mounted electric vane-type pump for each tank, pulling through a spin-on type filter.  A low-restriction check valve on the outlet of each pump allowed me to draw from either tank without filling the other.  But it worked well for over 20 years.

Then one of the pumps started losing its prime frequently a couple of years ago.  I replaced the pump twice, replaced the filter housing and filter, added additional tank vents, pressure-checked the system umpteen times looking for an air draw/leak, and finally drilled out the tank suction tube (see above), figuring that the suction tube was cracked inside of the tank where it attaches to the tank bung.  To say that I was severely disappointed when that didn't fix the problem would be the understatement of the decade.

So I switched to an old-fashioned mechanical pump, with a home-brew remote fuel switching valve to allow me to draw from one tank or the other.  Problem solved, and I still have no clue as to why I couldn't get the original system to work again.

Good luck with yours!