Re: Electric fuel pump vs original mechanical fuel pump

Posted by HH56 On 2021/11/23 11:04:51

Assuming you are using the solenoid type electric pump that mechanical pumps can pull thru when the electric is off, It seems the 6v aftermarket pumps are only available with 5/16 ports. One issue another poster ran into with a different engine is in a pump with 5/16 ports, the fuel passages inside the electric pump are actually smaller than the advertised size. That could be causing the starving issue when the pump is off but with flooding when the pump is on, I would wonder what the actual output pressure might be. Perhaps the pump is faulty or labeled wrong. Not sure if a 12v pump would be the best if the rest of the car is still 6v but Airtex does make a relatively low pressure model (5-9 psi) with 3/8 ports. That high end number is pushing it for a carb even if the pump is located by the fuel tank and pushing thru filters etc so there might still need to be a pressure regulator in the line.

On the starving issue, he tried a different brand 5/16 pump with similar results. I think his fix was to rig a pair of tees to bypass around the pump similar to what is needed with a rotary pump only using a larger diameter check valve. Don't remember if he used 3/8 or 1/2 for the bypass and check valve but by using that and what fuel still flows thru the electric pump when it is off the mechanical pump could pull thru at about the same capacity as the normal intact 5/16 fuel line. If you try something like that be sure to get a check valve with the lowest minimal opening pressure you can find. Most are around 1 psi but some specialty valves can be found that are rated at about half that.