Racor primary fuel filter vacuum diagnostics

A Racor primary filter vacuum gauge reading tells you where fuel restriction is happening. Normal reading at idle: 0-2 inHg. Under cruise load: 3-6 inHg. Above 8 inHg indicates restriction. Above 10 inHg the engine will start losing power at load. If vacuum spikes only in rough water, the pickup is drawing air, check anti-siphon valve, tank vent, and pickup tube depth. If vacuum climbs gradually over hours, the filter element is loading, replace at 8 inHg. If vacuum is high immediately after a filter change, check for a pinched fuel line, closed valve, or crushed tank pickup screen. Racor 900 series uses 30-micron for primary, 2-micron for secondary. On dual-Racor setups, always start with only one selected to isolate a bad filter. Water in the bowl is normal in small amounts, drain via the petcock daily during operation.