I am a bit confused by Bob M. and Jeff E.

 

In a carbureted aircraft engine configuration, the only use of an adjunct pump (hand or electric) is to supply some priming fuel directly to the intake side of a cold engine before start.  The engine driven pump generally provides a constant pressure fuel supply at about 4-6 psi (maybe less) to the bowl until the float says stop.  The carb doesn't care if the fuel is sputtering into the bowl with vapors since the fuel level in the bowl is all that counts and that level is kept ahead of the actual carb's needs.  Oh yeah, gravity supplied fuel to a carb works too - as long as there is fuel in the bowl.

 

On the other hand, a fuel injected engine, say a Lyc 320 with an RSA style fuel system, generally requires that some level of fuel pressure must be maintained so the stinking throttle body can match it to the air via pressure measured by some weenie tubes in the induction stream so that ultimately it can deliver the correct fuel flow to the injectors.  The ideal pressure is about 26 psi, but the system only gets upset if the pressure drops below 12 psi (fluctuations between those values don't seem to make much difference).  How can such variation happen?  Well, one way is vaporization of the fuel because of heat and thus cavitation in the engine driven pump, especially if that pump is also heat saturated from the engine operation. 

 

How can that be fixed?  Cool fuel could help or maybe raise the system fuel pressure (read boost pump) to try to keep the fuel from vaporizing before you actually would like it to vaporize, like near the intake valve.  The "hi" boost pump in my airplane could maybe get the fuel pressure up to 28 psi, not much higher than the engine pump operating on cool fuel but high enough to get the fuel back to a liquid state.

 

Another way to solve a pressure problem traced to the engine pump might be to duct some cool intake air over the engine pump - if that is the source of fuel pressure loss/fluctuation during flight.

 

The only times I have problems with vaporization is during a hot start or idling/taxiing very slowly on a really hot day - my red idiot light labeled lo fuel pressure comes on and is backed up by the fuel pressure gauge dipping below 12 psi, a condition that has been resolved by turning on the boost pump.

 

BTW, the boost pump is on for takeoffs and landings as a backup.