It's injected. So it's not the same as N/A. You need the vent the same size or the next size bigger than the outlet (as was mentioned in another post) and that is the MINIMUM it needs to be.
Also, it's alcohol. You have to remember that fuel is being returned to the tank. So because it's injected alcohol and has a return line, you need a BIG vent. Alcohol producers more vapor in the tank when return fuel is put back into the tank.
And vapor creates more pressure in the tank
Have you ever run injectors? I ask, because every time I pressurized the inlet side of the pump, you couldn't tune it, and the tune changed in proportion to the pressure above the outlet.
Also, (this is way over my head but it's what happens) any air entrained in the fuel in the tank from bypass fuel is stays in the fuel, which alters pump output.
Big vent. If you are having tune up issues, look at the size of your vent.
