Originally Posted by alpha
What is the reason for this check valve ?
Used where the engine is higher than the fuel tank. When the fuel pump is not running, some systems may allow fuel to run back to the tank, causing slow starting or possible damage to fuel pumps??
AFAIK, the check valve is a non-return valve to combat the above. It is bound to restrict flow a little. So would a slightly clogged fuel filter, a filter that is too fine a mesh or simply too many filters in-line. See also crushed fuel pipe, clogged lift pipe etc. What have you tested so far?