Chip,


With a muffler pressure system, that would be wrong!

As the engine is throttled down, excess pressure in the tank is vented back into the muffler.
If you put a one-way valve there, there would be too much fuel pressure at part throttle/idle and the engine could be dowsed and die...

You need maximum pressure only at maximum throttle.

A small engine with a large tank is more likely to die, as the throttle is snapped shut, since it takes too long for the tank pressure to be vented; even if there isn't a one-way valve on the exhaust pressure line. A one-way valve will only make matters worse.