dude im a idiot but we had a fuel problem for the whole season. someone posted if you unscrew the fuel cap it should have vacuum in the tank. mine didnt, so replaced the one way valves. they did have blow by in them and for the one ways should work one way but not the other. mine worked both ways. bought some at big A autoparts. Went back out all excited guess what dies after in hour. Unscrewed gas cap, still no vacuum. Found out the damn gas cap didt have a oring or gasket on it. I put my hand over the fuel tank outlet fired right up. just my experience.
Pretty sure it's suppose to have pressure, not vacuum.
Too much pressure can overwhelm the needles and seats and cause leaking venturis. However, a vacuum, or even a low pressure, can starve the motor of fuel. If the vacuum in the tank is higher than the suction from the fuel pumps, your motor will be starved for fuel. This need grows as engine RPM increases and causes the most problems at high RPM. It can also cause leaning and motor damage since the fuel delivery will be different than that which it is tuned for. This is no different than a clogged fuel line/petcock/filter.
Your one-way valve lets air in, while preventing air and fuel from getting out.
My Superjet always has pressure. It runs well. My X2 has no pressure. It also runs very well.
Vacuum = staving (if too high)
Pressure = leaking venturis (if too high)
