Date registered: Feb 2007
Vehicle: '74 & '78 450 SEL
Mentioned: 3 Post(s)
Quoted: 750 Post(s)
As already stated, you'll need to crimp the fuel lines to avoid spilling fuel everywhere when you disconnect them. I recently replaced my fuel pump, filter and changed the screen at the fuel tank outlet and discovered that the fuel lines were rotted and they split when I clamped them tight, resulting in gallons of fuel on the ground (and in my hair and clothes).
If your car has been sitting for a couple of years, it's possible the gas in the tank has deteriorated and is the major cause of the engine running poorly. If you drain the tank at the same time you replace the filter (and fuel lines, if necessary), then you fix two potential problems at once.