Or I guess you could have a crack in your 3-way valve. I've seen that happen too. Water could have been in the closed section and it froze over the winter. That would explain why one way works fine and the other doesn't hold pressure.
One cheap way to see if you have air bubbles being drawn into the fuel line is to get a small loop of clear tubing and insert it in your fuel line. Barb one end of the loop with a male barb. Disconnect the fuel line from the tank and connect the clear tube between the tank and your regular fuel line. Repeat after the 3-way and after the racor. You will see the air bubbles in the clear line if there is an air leak. That will pinpoint where your problem is if its an air leak.
I picked up an electric helper pump last night and Im going to get a new motor pump as well this week. I replaced the "T" as well. I'll take it for a spin this weekend and see if the symptoms improved.
Makin fur fins and feathers fly.
Replaced the T fitting with a new brass one. Added an electric helper pump and got another 1/4 turn out of the fitting on top of the tank.
I had to pull the "helper" pump out because it wasn't pushing the advertised fuel load. By tying both tanks together and removing that odd ball vent that was in by the fuel filter the boat will run to full RPM now. I was able to push all 4400 rpm out of it on the lake and ran it for about 15-20 minutes in circles with no issue.
The only problem I have now is the idle wants to be a little low. I may need to adjust the carb to give me a few hundred more rpm at idle so it doen't choke out.
So to summarize: Added a new smaller diameter pickup tube inside the old one. Replaced tank top fitting and "t" fitting, replaced fuel line, removed vent in front of fuel filter.
Makin fur fins and feathers fly.