from here
172 vs 177? - CESSNA 172 FORUM - Cessna 172 talk 24/7
In cruise flight, the Cardinal is a steady IFR airplane—if you can get it trimmed out laterally and keep the fuel balanced. Several owners reported gross fuel-flow discrepancies when the fuel selector is on “both,” with the tendency for fuel to flow from the left wing. Left-right switching every half hour may be necessary to maintain good lateral trim or a few seconds of uncoordinated flight to clear the liquid from tank vent system, which is what causes the imbalance.