I have been fighting with my vacuum pump system in my M2 1928 Rugby. The Stewart is the model without levers. Gas flows from main tank to vacuum pump, but gas do not flow evenly from vacuum tank to carburetor, it flows, but after a long while carburetor gets out of gas, as if the flow is not enough. All piping is clean and gas and vacuum valves of the Stewart lid operate correctly. I think that flapper valve do not seal enough, or that vent hole of outer shell is not big enough. In my model, the vent inlet of the vent valve does not connect to the environment as shown in manuals, but connect by means of a copper tube to the outer shell, and the outer shell has a vent connection.
My questions are, how much tight should seal the flapper valve and how big should be the vent hole.
Sucking with the mouth vent valve after closing the gas discharge valve, some sucking from vent valve is observed, flapper valve should not leak at all?
Gas flows neatly from the main tank to the vacuum tank, noise is heard clearly still after the engine stops for lack of gas.
Somebody can give an advise?, no local repair for this system and not very practical to send it to repair to the US as I am in Argentina.
I had the same problem with my car starving for gas and it turned out to be the screen on the inlet to the carb was plugged. After I cleaned it the problem was solved.
Sory Jan for my late response. I have not seen your answer. Based on all the advises and available documents, and a lot of perseveration, my Stewart is working nicely.