'78 merc 1400 fuel pump/fuel lines

This topic is about the L6 engines with single fuel pump...i've seen several topics on this saying these fuel pumps were marginal in fuel delivery...seen a thread last night and someone said to use 3/8ths inside dia. fuel lines...WELL, the fuel pumps have an inlet fitting that is only 1/4" inside dia. and the outlet side of the pump is the same size...if the size of the line into the pump is small and the outlet fittings are small...why would one think that increasing the size of the fuel lines would help anything if it is already restricted at the inlet and outlet fittings on the pump...increasing the inside diameter of the fuel lines from the pump to the carbs is only creating more volume that the pump has to try and make up for...

Re: '78 merc 1400 fuel pump/fuel lines

The OEM fuel line size was 5/16". 3/8" is better since it will have less resistance to flow. If you have a 1/4" fuel pump, you might check part numbers, to see if it is the correct one.

Re: '78 merc 1400 fuel pump/fuel lines

Thanks Chris...I was calling you out on that one..LOL...!! And yes, my lines are factory lines at 5/16ths I.D. but what i was refering to on the 1/4 inch measurement was that the I.D. of the pump inlets and outlets....which, i just measured again, and they are actually only 3/16ths I.D....that just seems way tiny to me to be able to feed that L6...any ideas on improvements here..? what about an electric pump...

Re: '78 merc 1400 fuel pump/fuel lines

Part of the deal is the restrictions are only a very short piece of the overall length so they do not affect the flow near as much as a small diameter fuel line. Is there enough material to drill out the inlet? If so that may help, but I wonder if someone put the wrong pump on to begin with.