I had a Jaguar where the intake manifold filled with gas and the cause was the gas could not return to the tank. In other words the return line must be blocked. The excess gas fills the manifold. On the Jag it had 2 gas tanks and a valve which was supposed let the fuel back to the tank failed so all the gas went to the other tank and when that filled up the intake manifold filled. Just guessing your return line may be blocked.