If you do mod your fuel tank lid to take more volume, your tank will be bigger as to volume and you will be over 125ml and you get a penalty according to rules... So, this might cure your problem, but will get you out of the race :-(
Team Orion used to make a pressure regulator for the backpressure. You could adjust the pressure from the pipe, when the enigine wen`t to idle, you still had the high pressure in your tank. I liked the idea, bought one but never got aroaund to test it.
I have had experience with your problem before, but on the two times i have seen this, it is soemthing inside the high end needle blocking and opening the hole on the needleseat. This hacve happend at big races were my fueltank have been messured for volume. You can clearly see it when you take the high end needle out. It has a small silverline aroaund the needle, a scratch. flushed out with fuel and fixed the problem.
I wasn't talking about modding the lid. More pointing out that overfilling your tank will force fuel up your fuel line, specially with tanks that have little space in the lid
