Another valve on the tank top is still closed, Restricted fuel pick up, damaged or smashed copper line from the tank. Are you drawing air from the tank? Are you watching your vacuum gauge dive? Are you sure of the selector valve position? Been on a few boats where they are poorly labeled and bass ackwards from port/stb engines. Any other service valves (after mfg) that need to be checked?
If the valve is correctly marked then not that. Mechanic buddy just told me he will bring over a fuel pump with a bunch of adaptor fittings so I can disconnect the feed line to the valve and see if it will suck fuel and if good there, then hook pump to the other side of the valve.
Could be a check valve in the pickup. Honestly, I'd disconnect hose at tank pickup and start there and see if you can get fuel out of the tank at the tank...........could be fuel line is collapsing as well.
Sounds like you have a tank load of old dirty snotty fuel , if the previous owner never used that tank, and now you are just getting to use it, who really knows how old it is. I would say the line/pick up tube is plugged up. Start at the tank where the tank shut off valve is. Remove the fuel line from the shut off valve and blow a good puff of air from a small air compressor, or put a new hunk of clean tight fitting hose to the open valve and blow down carefully with your mouth and listen for bubbles of air with in the tank, make sure it's free and clear. Then work your way back wards to the Racor filter, removing one hose at a time and blow air through them to make sure they are clear. You will be able to blow the diesel snot out of them with the air compressor if they are plugged up. Blow through your valves with the line off. Make sure you feel air or not in the supposed open and closed positions. Your buddy and his fitting trying to suck fuel through many not really work. You have to clear things out with good puff or air. Make sure you have a few oil zorb pads lightly folded over the open discharge side end of the hose to capture fuel and snot. I had to blow out my Starboard tank pick up a few times over the years due to a top of tank water leak from the previous owner. Took me a number of tank loads over time to clean up the tank. Had to unclog the generator pick up tube many times, back flushing it with air to blow the junk out. Things are finally better now. You may want to get the tank/fuel cleaned and polished. But that only works so well.
Back in previous life I spent a bunch of time on a buddies 44 Striker that I guess was like a small ship when it came to the tanks. Each had a round man sized diameter hatch. Not yet looked. I Ordered a couple new Suzuki's for the 25' and will have to deliver to them on trailer when they call so playing catch up on some trailer neglect.
Great in head sea and also stable. After owner died was unable to find where the 44 went so gave up thoughts of buying her. Was considering buying one in Ca. last year but decided on a local Bertram instead. Striker told me they discontinued due to lack of profit and only build much larger now.
I found a 44 in S FL a couple of months ago. Josie threatened to really KoBong!! me if I thought any more about another boat.
Found a pic. Here is that 44 that I managed. Un-loading her of stuff to pull up the deck plates over the engines. That recliner went and stayed on my back porch. Most of what other came out was trashed. Amazing how well boats run empty of stuff.. Got lots of fuel tank stories on this boat. That was my dock on the Trout River, Jax FL. My 28 Trophy in the lift. This would be around 1988/89
Last thing I need is another boat. The seller of the Bertram had just turned 82 and said it was getting to be too much. Not there yet but starting to relate to the too much.
Yep, Our Bert getting to be a hand full. Got the bright idea for some interior re-arranging last October. That was a mistake. Been window shopping for another 28 Trophy since I found that picture.. Shame, none around. Well, maybe good,,, I'd get KaBonged for finding one. That was a fun boat.
I've managed and run a few. A 58' and a 62'. They were always basket cases. Off the wall equipment for many things, so hard to find parts for. The tankage sucked.....they had 3 tanks and middle was a day tank......had to open a valve from the foward or aft tank, but needed to be on plane to empty the forward tank........and at trolling speeds to empty stern tank.......The ride wasn't great, it was ok to good, but not great........and somewhat wet.
I never ever trust a fuel gauge. Never. The only way to be sure of what you have is either to use a calibrated stick or a sight gauge. and when tanks have an odd shape, like some keel tanks, the only way to be sure is to calibrate the fuel stick while refueling. I did that on my Hatt years ago. Starting with very low tanks I marked a stick every 25 gallons while fueling. Lazzara included an engraved calibrated stick for their main tanks. As to fuel pick ups, if you know your usable fuel capacity, it s no big deal to have the pick up a couple of inches up. On my boat I use a piece of copper pipe connected to a filter and electric pump to suck and clean the bottom if need be