Having two throttle return...
Having two throttle return springs is the best way to go. Be sure the springs are mounted properly, and check them frequently.
13 Filtering of fuel cell vents Just as an undersized vent will adversely affect your fuel system, not having a filter on the vent will cause dirt and debris to enter it. As air replaces the fuel, the vent hose will attract anything that's in the air, including dirt, sand, or debris. These particles will eventually destroy a fuel system as well as an engine.
14 Fuel filter location To protect the fuel pump and carburetor, use a good filter between the tank and fuel pump, and filtered fittings at the carburetor.
15 Inspections Steel braided fittings and aluminum fittings have a life cycle. Over a period of time, the rubber bore will deteriorate, causing the line to either collapse and starve the engine of fuel, or disintegrate and possibly block the passage. Radiator hoses and fan belts are routinely replaced. The same thinking holds true for fuel system components. From a safety and performance standpoint, regularly check the lines and fittings. Try to detect soft or weak spots by feeling the outside of the lines, and visually inspect the internals each season. Keep the connections tight.
The air quality makes a huge difference in the fuel system's production. A well-made and well-maintained air filter of adequate size will improve performance.
You can overcome sizing problems with a removable sleeve model when picking a carburetor. This two-barrel Demon has one sleeve installed for illustration purposes. Several sleeve sizes are available.
This is the schematic of a system that uses a throttle bypass.
This fuel system uses a belt-driven fuel pump with diaphragm bypass.