Vacuum Test
Disconnect fuel inlet line at fuel pump and connect vacuum gauge to pump inlet fitting. Disconnect pump outlet line, to ensure pump operation at full capacity. Crank or run engine at 500 RPM and note gauge reading and reaction. Vacuum should be 10" Hg. at 500 RPM and gauge needle should remain steady.
NOTE:
Blow-back or immediate drop when pump is stopped indicates inlet valve is not seating (except on internal bleed-off type pumps).
Incorrect fuel pressure and low volume (capacity or flow rate) will affect engine performance. Low pressure will cause a lean mixture and fuel starvation at high speeds. Excessive pressure will cause high fuel consumption and carburetor flooding. If fuel pump pressure, volume (capacity), or vacuum, is not within specification, and no other defect in fuel supply system is apparent, overhaul or replace fuel pump as required.