5/16” push lock fuel hose fittings

If it were me I would change them without question.  The AN-6 minimum size requirement is important on the 912iS engine. The fuel pump(s) will circulate upwards of 28 gallons per hour during normal operation.  Smaller than specified fuel lines on the inlet side of the pump may induce fuel vaporization and pump cavitation.  On the return line, AN-6 lines are specified to assure the return line pressure remains below 7.25 PSI (after the fuel pressure regulator). Higher return line pressure will interfere with the proper operation of the fuel pressure regulator. 

If you want to see how much a small change in fuel line size affects things, check out this fuel line calculator. The default settings on this calculator are for 15’ of AN-6 line (.375”) and a fuel flow of 600 lbs/hour. If you change the fuel flow rate to 168 lbs/hour, that represents a 28 GPH flow - close enough to represent a typical 912iS installation.  Go to the bottom and click on calculate then note the pressure drop and fuel velocity.  Now change the fuel line size to 5/16” (.3125”) and recalculate.  You will see about 50% more pressure drop and similar increase in fuel velocity. Now consider that this pressure drop affects the inlet side of the pump as well, where the fuel may already be under a slight vacuum (suction). The lower the line pressure is at the pump inlet, the easier it is for the fuel to vaporize before it enters the pump.

https://lmengines.com/pages/fuel-line-calculator