I went to get the bike dyno tuned today and the first thing they did was "T" into the fuel line and hit handle bar switch to pressurize the fuel pressure. The gage read 40 psi, then quickly dropped off. They told me they could not tune the bike as the pressure should have been 50 psi minimum, and it should have held longer. Does this make sense? On a Dyna (FXDL), what is the most likely culprit if there is a problem? The bike has 25K miles, and I was going to remove the dash to replace the fuel filter anyway.

 

I would say 1 of 2 things might be causing your issue.

1.) cracked fuel filter
2.) deteriorated fuel line inside the tank.

don't replace any fuel line with cheap stuff from the auto store. go get the OEM fuel lines. they're designed to hold up to the high pressures of your fuel system.