Since the subject of these posts is about getting a steady and reliable engine run ( with different tank set ups ), I thought I would comment on what I did back in the early 1980's. I wanted to build a Slow Combat airplane that would do 100 MPH and maneuver well. I had a fairly good knowledge of making the engines go fast but was just guessing on a suction tank set up. I started with a Fox wedge style tank and cut out a section of the outer wedge to fit in a #2 Perfect tank as a "hopper". Using a sharp ice pick, holes were punched in the front and the rear of the perfect tank which were on the inside of the wedge of the Fox tank. This allowed fuel to get inside of the Perfect "hopper" tank. The fuel feed line to the engine exited the perfect tank in its usual position. A fill and overflow were soldered into the upper front outside of the tank and when the tank was full, these were connected with a piece of fuel line. So now we need a vent. I always saw tanks with the vent facing into the slipstream, which I assume would add some pressure to forcing the fuel out of the tank and into the engine. Well, I did something different. I put the vent tube exiting the BACK of the tank. The other end went into the Perfect "hopper" tank. Right into the middle of the tank. The venturi restrictor that came with the Fox .36 MK IV engine was tapered with a tapered prop reamer. From the top to the spray bar hole and then from the bottom to the spray bar hole. This would maximize the suction with the fuel draw. After a few flights we ended up raising the tank 5/16" above the center line of the venturi to get steady runs ( and not go rich ) in the outside maneuvers and we had what we wanted: a steady run for the ENTIRE flight. When the tank was empty it did not give you ANY warning that you were running out of fuel; the engine just cut off. I am guessing with the tank vent coming out of the rear of the tank ( facing to the rear of the airplane ) that it was in a negative pressure area. I never had an airplane with as steady a run as this one had. And yes, it would go 98-100 MPH anytime you threw it in the air.
Dick Tyndall