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Fuel pumps on macs

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  • Fuel pumps on macs

    Yes the issue with the Mac 72 was a fuel pump issue. This is why it would not stay running. The question is will a rebuilt Mac fuel pump be reliable. Can you have an inline backup vacuum pump T'ed off with the Mac pump. If not in both cases what is the best way. There's probably alot of pump options.

  • #2
    I was told not to run the Mac fuel pump and to go with a pulse pump
    David Bacon

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    • #3
      Yes. I have read on the forum that the AC Delco mech. fuel pump that McCulloch used was only meant to last for a few hours or not many hours for the drone applications it was used for. You would think it would last like any other pump. Some of the experienced Mac fliers I communicated with said pulse pumps were more reliable.

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      • #4
        IIR, Bensen specified a backup fuel-delivery system that employed the crankcase-compression pulses directly. It fed these pressure pulses through check valves into the tank itself, pressurizing it.

        I believe that this system was enthusiastically cursed by many who used it.

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        • #5
          Mechanical fuel pumps didnít last long on a Mac because they ran at crankshaft speed, -4,000 rpm rather than at camshaft speed when used on an automobile.

          I used OMC outboard pulse pumps with good results before Mikuni pumps were generally available.

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          • #6
            My fuel pump sits under the motor and runs off a rod from the crankshaft. The outlet of the pump runs to a regulator and then to the carb. I put a guage between the outlet of the regulator and the carb. The system has plenty of pressure and I have had no problems with it.

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            • #7
              Would like hear how long your mech. fuel pump lasts on a Mac.

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              • #8
                Long enough to get you into the pattern. Then its a Mac Attack!!!
                David McCutchen
                615-390-2228
                Bensen B7m, 90 hp Mac
                Dominator Tandem, 100 hp Hirth
                Kolb Mark III Classic, 80 hp Verner
                Certified - Advanced Master Beef Producer
                EAA Member #0511805
                PRA Member #28866
                PRA Chapter 16 Member
                Secretary & Treasure - PRA Chapter 16
                President / Sylvia - Yellow Creek Volunteer Fire Dept.
                Chairmen - Dickson County Veteran's Day Committee
                Volunteer - Dickson County Airport Aviation Day Committee
                2 busy 2 No!

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