No power from 50 mls and up

Discussion in 'Street/strip 400/430/455' started by colonel, Aug 11, 2021.

  1. colonel

    colonel Speedjunky

    I finally got around routing a 3/8" fuel hose with a transparent fuel filter from the fuel hard line to the windshield and back to the fuel pump. The fuel filter was right in front of me when driving.

    Upon start up and idling, the pump filled the fuel filter (approx. 2" in dia and 4" long) about half up to the middle. I did a test run, cruising around town with a couple of kickdowns and finally to highway speed around 60-70 mls per hour. The symptoms came back from 50 mph and up.

    I noticed two things:

    #1 The stream of gas is not a continous one. Sometimes it´s a thick, hard stream, sometimes no fuel at all, sometimes a slow stream, sometimes "spitting". I did not notice a direct correlation between how the fuel was delivered and what position the gas pedal is at. Is this normal? I never gave thought to how EXACTLY the fuel is delivered to the carb and could imagine that engine vacuum and fuel level in the carb bowl play a role also, not only engine speed (i.e. revs, i.e. fuel pump lever movement).

    #2 At higher speed, the fuel level in the filter was VERY low, lower than the paper element. That was when the car started acting up. So apparently the engine pulls more gas than the pump can deliver (for some reason).

    Any ideas to the above?

    I do have to admit that the 3/8" fuel hose might have gotten a little squeezed between the hood and the rubber seal at the rear of the engine bay, but I don´t think this compromised the test run too much.
  2. rkammer

    rkammer Silver Level contributor

    Your testing still indicates a fuel delivery problem. You still need to take the tank down and inspect the fuel sock within the tank. Also, it hasn't been mentioned that there is a rubber section of fuel line that bridges the steel line located inside the frame rail under the driver's door. Check that for deterioration too.
    69GS430/TKX likes this.
  3. colonel

    colonel Speedjunky

    Yes, fuel delivering problem. I repeated the test drive with the gas cap off, no change.

    As my gas gauge doesn´t work (full to the right side) I wonder if I should replace the sending unit, once the tank is down? The unit has a good ground and if I ground the wire TO the sending unit, no movement of the needle either. At the same time, I know I have a dash electric problem (no dash illu, no left turn signal/hazard indicator light - right side ok), so not sure if it´s the unit or the wires/printed circuit.
  4. rkammer

    rkammer Silver Level contributor

    If you buy a new sending unit there will be a strainer sock included with it.
  5. LARRY70GS

    LARRY70GS a.k.a. "THE WIZARD" Staff Member

  6. colonel

    colonel Speedjunky

    Yap, found those items already, on the fence to order, just not sure if a sock will be enough? RA does not carry them, just complete sending units.

    I checked on (read: grounded) the tan wire once more today, nothing! This actually should mean the culprit is in the front harness, not the sending unit. The pink wire in the fuse block has +12V, but I need to locate the body connectors to check for continuity on any of the tan wires.
    Last edited: Sep 14, 2021
  7. 69GS430/TKX

    69GS430/TKX Silver Level contributor

    Could it be a bad fuel pump? One other possibility: The steel fuel line has rusted through, somewhere where it contacts the frame, and the hole is facing up so there won't be any leaking gas on the ground that would indicate trouble. With air coming into the fuel line from that rusted hole, the engine might be starved at higher rpms.
  8. colonel

    colonel Speedjunky

    No, I replaced the fuel pump last week or the week before, was my initial thought also. I will check for punctuations of the fuel lines when I drop the tank.

    I ordered a new sending unit and will drop it in next week or the week after, as soon as I get to it.

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