Hard to start after 2 days, fuel drain is possible. Why?

Discussion in 'Street/strip 400/430/455' started by Beamer, Feb 7, 2017.

  1. BQUICK

    BQUICK Gold Level Contributor

    So not having the clip would keep the needle in the seat and prevent drain back, correct?
     
  2. 8ad-f85

    8ad-f85 Well-Known Member

    Is that a trick question?
     
  3. carmantx

    carmantx Never Surrender

    Yes. seat would be seated when no fuel was flowing in to the carb.
     
  4. 8ad-f85

    8ad-f85 Well-Known Member

    Unless the brass seat is windowed, how is it possible to drain down below the top of it?
     
  5. garybuick

    garybuick Time Traveler

    so nowadays there is no disadvantage to removing that clip?
     
  6. carmantx

    carmantx Never Surrender

    No disadvantage to removing the clip, that I am aware of. Never had a known issue resulting from no clip.

    I always use a windowed seat, but without windowed seat, fuel wouldn't drain down below the top level through the seat.
     
  7. TORQUED455

    TORQUED455 Well-Known Member

    Mike, the absolute "correct" way to further diagnose the problem would be to use a vacuum gauge on the suction side of the fuel pump and at the suction line back at the fuel sending unit, one at a time of course. If the fuel pump is bad, you won't have a constant building of vacuum up to 4 or 5 inches when cranking when testing at the fuel pump. If you have a steady increase of vacuum at the fuel pump, and the needle doesn't bleed back down to 0 during cranking, then you repeat the test back at the sending unit. If there the is "good suction" at the pump and not "good suction" back at the sending unit, suspect a rotted rubber hose or other poor connection somewhere.

    I think that since you had a good pump shot with the line pinched-off for a couple of days, you may have a bad fuel pump. That may also explain why it took so long to pick the fuel back up from the tank too, after it started and ran for a little bit and quit. A mechanical fuel pump can have a bad check valve yet still perform well once it finally feeds fuel to the carb. You can also have a fuel pump with a bad check valve that DOESN'T perform well either.
     
  8. TORQUED455

    TORQUED455 Well-Known Member

    It doesn't matter whether the seat is windowed or not. If the needle is seated (aka full bowl) and if no clip is used, fuel evaporation from sitting won't allow the float to "open the front door" by pulling the needle off of the seat and let fuel possibly drain back also (double whammy for hard starting).
     
  9. 8ad-f85

    8ad-f85 Well-Known Member

    My question was rhetorical. It won't drain back below the height of the opening, windowed or not...at least not that way.
    There's always some in the carb unless leaked out elsewhere or evaporated.
    The obvious didn't escape me on the clip. :)

    I think everyone agrees that this is an easily solved basic maintenance and tuning issue if it were actually in front of them.

    [definitely some good info for newer enthusiasts to problem solving!]
     
    Last edited: Feb 24, 2017
  10. Beamer

    Beamer Suncoupes Rule !!!

    I wanted to update my current condition along with another test I had done before installing my calibrated built carb from Mark.

    I did test vacuum at the pump and saw it spiking to 6-7 inches of vacuum and then drop away. I never made it to the tank as my carb from Mark showed up and I was excited.

    I installed the carb from Mark with the supplied gasket. Following his directions, once I had the car started and running with the motor warmed up, I went to adjust the air/fuel mixtures. I used a vacuum gauge, but my cam only provided about 8 inches of vacuum and I did not think that was adequate so I went by the RPM method. He set the base to 2 turns. I turned it it until the motor started bogging down and backed each out to where the RPM stopped increasing. Which was just over 3 turns total (in 1.25 turns, out 2.25 turns). After I adjusted the air/fuel, I set the idle around 1050 or so. When I drop it in gear, I am sitting around 750-800. The car runs beautiful ! ! ! Crisp, smooth and no issues observed at all. Secondaries open quick and with no hesitation or bogging down.

    I let the car sit for 5 days. I don't care if there is no fuel in the bowl and don't try to start without cranking a few revolutions. I give 5 seconds of cranking the motor over. I hit the throttle 3-4 times and within a second of cranking again, she fires off and will run with very little throttle adjusting. The motor is very happy with this new carb I have on it now. After keeping the RPMs around 1500 for 30-40 seconds, the motor will idle on it's own. Just how I want it to be like. With 3-4 hours of driving, just a hit of the key, the motor will fire off and run on it's own.


    I am completely satisfied with this carb that Mark built for me.I thought I had a possible ignition issue, but he has discredited those thoughts.



    Mike
     
  11. 8ad-f85

    8ad-f85 Well-Known Member

    Glad to hear your carb is working better.
    Good news is that there is lots of room for improvement.
    It's going to start up even easier and run much stronger when you figure out why you only have 8" idle vac.
    Hooked up to the wrong source?
    Not enough initial timing?
    If it is truly caused by the cam being massively retarded you'll get a serious wake up upon correction.
    Get the timing curve dialed in and you'll see even stronger performance.
     
  12. Rob Ross

    Rob Ross Well-Known Member

    Something is wrong if you only have 8" of vacuum with the camshaft you posted. You should be more like 14" and if you're carb is properly modified and set, you should see < 200 rpm drop when you put in gear. Your idle mixture screws may not be set optimum.
     
  13. LARRY70GS

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

    Try another vacuum gauge. If you really had 8" of vacuum, you'd have problems with the power brakes.
     
  14. Beamer

    Beamer Suncoupes Rule !!!

    I will try another sometime, when I get a chance. I will say that I am quite happy with how the motor is running now. I am sitting at 36 degrees BTDC total advance. I can't recall what I was at idle, all mechanical though. The power brakes work just fine also. I did come off the port at the bottom and passenger side of the carb, from what I recall.


    Mike
     

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