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Evening all,

Not a particulary Packard question but one that can affect any vintage car.

Due to a rusty tank on my Dodge Bros, I have fitted several fuel filters over the past while, between the tank and the carb, before and after the pump, all in different positions and at various heights.

The question is where does air come from in the filter, I have used all types including a type which can be bled.

I have used non-return valves, checked for leaks but all to no avail.

Any ideas?

Pat.

Pat, I wonder if you have a pin hole leak in the gas pick-up tube inside the gas tank?

Thanks for you reply.

I have not got that far yet, also I have connected the inlet pipe to an outside petrol container, thus bypassing the tank fuel line and pick-up.

Today's gasoline is much more volatile due to alcohol/methanol mixed in and probably other blending considerations. This is evidenced by carb fuel bowls drying out after a few days.

Maybe this explains "air" in the filter bowl. As the gas evaporates out of the carb fuel bowl, this releases pressure on the needle due to float drop. Any residual pressure (even gravity) in the incoming fuel line would cause fuel to be transferred into the carb, but since the fuel pump is not running, fuel or alcohol state changes to vapor causing the fuel level in the filter bowl to drop being replaced by gasoline blend vapors, i.e., "air".

Craig

Quote:

And what is the result?

The result is no difference using an outside fuel tank.

I am trying to get my head around the fuel vapour theory, while I can see how it would occur, I dont think it applies here considering the various sizes and types of filters I have used.

The current filter is situated below the level of the tank, pump and carb, it is a glass type with the inlet and outlet situated on top of the filter. It also has a bleed valve on top to eliminate trapped air (or 'fumes').

Pat, Are you using good quality rubber line? Sometimes old rubber lines will allow air to pass through as will a poor connection if used over an unflared pipe.