I see your problem as you are creating a small amount of backpressure in the Right side-feed hose.
A column of gasoline produces about 1 psi for every 3ft of depth.
If your fuel tanks are (for the sake of argument) 6 feet above the gascolator, there is about 2 psi of pressure being produce by the fuel column.
Now let's assume your fuel tanks are 9 inches in depth.
That means that if one tank is empty and the other full, you will have about 1/4 psi of differential pressure.
If you let it sit on the ground long enough the full tank will cross feed to the empty tanks until they are both equal and half full.
When the engine is running, the bypass fuel flow entering the right side, only needs to produce 1/4 psi to stop the fuel from feeding from the right tank.
Once the left tank empties and the left fuel line starts to go dry, (just guessing here!!!) you might end up with a 3 ft fuel column in the half-empty left fuel hose and a 6 ft fuel column in the full right hose.
The 3 ft differential will now produce a full 1pis differential pressure and the right tank will begin flowing.
You probably will not run out of gas, but it sure will be scarry to test this theory!
There are two issues here.
You could join the two fuel tank feeds together BEFORE the Gascolator and connect this common fuel feed to one port on the gascolator and use the second port for the bypass fuel feed Only.
That would solve the imbalanced fuel feed issue.
The bypass feed to the gascolator is a problem in itself.
When the gas goes through the fuel pump, it is like shaking a can of soda.
When the shaken gas becomes depressurized as it squirts out of the bypass orifice, it "fizzes" and produces gas bubbles that really need to be vented and not recycled back to the gascolator.
The saving grace of the Carbureted engine is that it has a mini header tank in the form of the carb fuel bowls.
A momentary air bubble entering the fuel bowl will get vented out the fuel bowl vent and as long as the bubbles are not too large or coming too often, you will not notice that it is happening.
The fuel-injected engines are another story.
While the carb'd engine can tolerate a momentary fuel pressure loss, the fuel injectors are very sensitive to any pressure fluctuations.
The fuel bypass line needs to return to a vented location in the fuel system.
Or as a minimum, but not an ideal situation, there needs to be an electric Auxillary Fuel pump located BEFORE the gascolator.
The bubbles are Not AIR Bubbles, they are Fuel bubbles containing mostly Butane gas and can be collapsed under pressure back into their liquid state.
This will allow you to pressurize and collapse the fuel vapor bubbles in the event of a vapor lock situation.
A vent port can be added to almost any tank for under $3 by punching a 1/2" hole and installing a Fuel Fitting and Bushing.
