I'm not familiar with the internals of the valve you are using The Real Dogman but I understand whats happening, if you could have a check valve that when open will allow full flow (unrestrictive - this is hard to achieve as the check valve will have a press drop as a function of its operation in the flow direction) but when pressure tries to flow back the other way it is restricted rather than "checked".
Matching both ends of the fuel system may be an answer (although impractical) - if you had a hole in the centre of the check valve the same diameter as the carb needle then tank pressure would not drop off immediately after exhaust pressure disappears while off throttle but would "equalise" at a similar rate to which it feeds the carby, therefore not flooding the carby AS MUCH if engine stalls. I guess a REALLY long exhaust pressure line would do similar but in both directions, but you only want the restriction in an opposing direction to the check valve flow.
A parallel setup with two tees and two checkers with different ratings (spring tensions) may work, a soft spring in the direction of pressurising the tank, a stiff spring that bleeds excess pressure facing the other way. As a refrig engineer I could get a valve off the shelf that would be perfect but unfortunately it would weigh about four times that of the genny I'd be bolting it to (plus it may need 240volts!)
I've noticed its heaps worse in hot ambients, 35 degrees celcius plus and low RH and I get flame outs, high RH or below 35ish and she hangs in there