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Hi, the only way that fuel can be pushed out of the filler neck is if the tank is not venting. You need to check all of the vent lines and also the vent pipes into the tank for blockage. You should also replace the charcoal canister for the vapor system. The is not a fuel injection system problem or a fuel line problem this is a vapor line problem. I have seen the very small vapor pipes plug up with rust or with beads from the charcoal canister. There is a vent valve at the fuel tank that you should check. Not sure if that is what you are eferring to when you say "overpressure" valve.
Let me know if you have any questions.
Hi Chris, a blockage anywhere in the system that you illustrated in 47-110 can cause pressure in the tank. The tank needs to be able to vent. If there is a blockage in the expansion tank system or in the charcoal canister the pressure will build up in the tank. You can disconnect some of the lines and see if it allows the tank to breathe. You could start by disconnecting #51. If the problem goes away your problem is between 51 and the canister up front. If you still get pressure then your problem is between the tank and #51.
Let me know if you need anything else.
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