Just as fuel evaporating from the carburetor bowl leaves a residue in the carburetor bowl, long periods on no use allow the fuel to evaporate from the fuel line also leaving a residue which adhers to the side of the line.
When any portion of the system is modified (i.e. removing/replacing a carburetor, fuel pump, or tank, the fittings on the fuel line are disturbed, dislodging some of the residue.
A GOOD insurance policy is to flush the lines by connecting a hose to the line before the carburetor, and cranking the engine (with coil disconnected) for about 30 seconds any time fuel system maintenance occurs. Pump the fuel into a can. You can then filter the fuel, and dump it back into the tank.
Jon.
