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Thread: fuel pump- mechanical, electric, both?

  1. #1
    Registered User MarkS30's Avatar
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    Default fuel pump- mechanical, electric, both?

    Hi guys, I have a '73 240Z that I recently switched from downdraft dgv webers that the car had to '72 roundtop SU carbs. i installed a new mechanical fuel pump, and also am aware that '73+ Z's had an electric fuel pump sometimes installed near the gas tank. I removed that (electric pump) recently, eventhough it looked fairly new. so currently the car is running on a new mechanical fuel pump only.

    all other things equal, this should be fine right? im assuming it would be as 70-72 Z's didn't have to run an electric pump. i did a little research here and am assuming the electric pump was only to alleviate some vapor lock issues the flattop SU's had.

    thanks,

    -Mark

  2. #2
    240Z Elec. Upgrade guy Zs-ondabrain's Avatar
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    The electric fuel pump is better for priming the carbs where as the mechanical takes a little longer. So if you find your cranking the car longer than usual to get her started, it's likely the lack of the electric fuel pump, is to blame.
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    Registered User MarkS30's Avatar
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    so far, it seems to start up the same. im guessing on the road there shouldn't be much difference either?

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    Semi-retired admin Arne's Avatar
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    I shouldn't think so. My '71 runs fine on just the mechanical fuel pump.
    Arne - Former owner, HLS30-37705, 7/71, 905 Red
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    Dave's point about priming the carbs presumably only involves getting the float bowls full faster if they are low. If the engine has run recently it should start right up in either case. Unlike fuel injection which requires the higher pressure of an electric pump the mechanical pump just has to be able to pump enough volume to keep the bowls full. Unless the car hesitates under a heavy load then the mechanical pump by itself is sufficient.
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    Default Mike, i agree with you...........

    Quote Originally Posted by MikeW View Post
    Dave's point about priming the carbs presumably only involves getting the float bowls full faster if they are low. If the engine has run recently it should start right up in either case. Unlike fuel injection which requires the higher pressure of an electric pump the mechanical pump just has to be able to pump enough volume to keep the bowls full. Unless the car hesitates under a heavy load then the mechanical pump by itself is sufficient.
    I use the electric pump only in summer time to keep enough volume in the bowls because of percolating problems over 100 degrees. In normal climatic condition, the mechanical pumps is never an issue.
    richard1

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    Registered User MarkS30's Avatar
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    thanks everyone for your advice. tomorrow when i have time, ill take the car out for a long drive. if nothing seems different, i'll leave the electric pump off.

    but....

    the wishy-washy part of me wants to put it back on, even if there is no difference, just for peace of mind that the float bowls are full before i start up the car. it was kind of satisfying getting used to hearing the pump hum for a few seconds, then finally cranking her over when i take her out.

    i don't know.... my apologies for my rambling.

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    I still use both pumps in the '73 with round tops and a 2.8 engine.

    The only time I had trouble with it was when the electric pump got unhooked while out on the track, then it had trouble with fuel starvation. Maybe the mech pump had trouble pulling fuel through the electric pump. So I still use both pumps so I won't have any trouble on the street or the track.
    things will only bother you if you let them.

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    Registered User hd240z's Avatar
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    I added an electric pump to my 71 and it primes the carbs faster after storage. I run both pumps during normal driving without any problems. I did add an inertia switch to cut off the electric pump in case of a crash.
    71 240Z HLS30 021986 (2/71 build) with 63,XXX miles

  10. #10
    Registered User MarkS30's Avatar
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    well, i drove it today with the mechanical pump only and it was fine. but for peace of mind, this afternoon i put the electric pump back on with a few filter. the end, lol.

    i appreciate everybodys responses.

    -Mark

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    FWIW, on my '73 I only use the electric pump. I blocked off the mechanical port. I did this in my quest to eliminate vapor locking. Its bad here in Texas in the summer. I could hear the fuel boiling inside the mech fuel pump. For shutoff, I used a oil pressure switch.
    Don
    Don
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