As Andrew says, my Walbro GSL393 pumps (from Tracy, before he retired) say '20 Amp Fuse' right on the pump. If you don't already know this, an automotive blade fuse is a relatively fast blow device; it will blow at the slightest provocation. 'Aircraft quality' circuit breakers, on the other hand, are basically 'extremely slow blow' devices. They can take seconds to trip, unless the overload is extreme.

The nature of blade fuses is probably why Walbro specs 20 amp fuses; the load on the positive displacement pump is going to be changing constantly with injectors opening/closing, fuel lines expanding/contracting, mechanical regulator opening/closing, etc.

If you're using a different pump, the equation might change. I've got some little in-tank turbine pumps I'm playing with that only draw about 6 amps at full load. BTW, there's a recent thread on the VAF forum about electrical architecture surrounding the new (to Lyc drivers) automotive style injection, where one of the really smart contributors, who's done both Lyc and alt engine installs, makes the case that 'switchology' would be safer it it's as close as possible to conventional a/c techniques. He advocates that the primary pump have protection, but come up with the engine controller automatically, and only the backup pump get a separate switch. (Different subject; may start a new thread...)

Charlie