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Thread: 73.5 CIS cold start

  1. #1
    Member #2634 Mac911's Avatar
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    73.5 CIS cold start

    Good Morning:

    I have a 73.5 CIS. I went out yesterday to drive my car and as usual I turned the key to on position, heard the fuel pump turn on. I then lifted the hand lever all the way up, NO pedal at all, started the car, I then put lever where car sounded like it was idling properly.

    I then noticed the smell of gas. I looked into the engine bay and there was no evidence of gas leaking. I then looked under the drivers side and saw a small puddle of gas underneath drivers side and gas was lightly spraying. Pushed the lever down and turned off the ignition. No more gas leaking.

    I went out an hour later and started the car (bypassing the cold start) by turning it on, heard the fuel pump and gave the accelerator a few half presses and it started. No gas leaking and seemed normal. The only difference is starting procedure this time was not using the cold start lever. I started it this again this morning. (Bypassing the cold start)

    I'm not one to try to replicate the problem. I didn't try the cold start lever again. Any thoughts of what I may be facing?

  2. #2
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    Pressing the gas pedal and pulling on the throttle lever do the same thing, including actuating the cold start system. If the throttle lever is up (or the accel pedal depressed) while the engine is cranking, the cold start valve is actuated.

    That said, although this only seemed to happen once, it sounds like you have a gas leak leak. Was the fuel leak at the rear? That's where the fuel pump is, and my guess would be a leak on the pump output (high pressure) hose. But you really need to get under there and have a good close look. Keep a fire extinguisher close at hand.
    --Richard
    Early 911S Registry #2337

  3. #3
    Member #2634 Mac911's Avatar
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    Hi Richard:
    Thank you for that info. It came from the center rear of the car. I'm checking the fuel pump and hoses ASAP. I really do need to get a Fire Extinguisher for my car. I wonder why it didn't leak gas the second time I tried it without the throttle lever?

  4. #4
    Senior Member mohrgan's Avatar
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    Check the vacuum line on the back left side of the airbox. I had the same problem with my car this past summer and the hose was disconnected and leaked when the hand throttle was activated and the engine was cold. When the car warmed up a little it stopped leaking.
    -Chris Mohr

    S Registry #1978

  5. #5
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    Quote Originally Posted by Mac911 View Post
    Hi Richard:
    Thank you for that info. It came from the center rear of the car. I'm checking the fuel pump and hoses ASAP. I really do need to get a Fire Extinguisher for my car. I wonder why it didn't leak gas the second time I tried it without the throttle lever?
    I'm not sure why it didn't leak on subsequent starts. The only difference it makes when the cold start system is actuated is that fuel is sprayed into the back of the airbox via the cold start valve to richen the air/fuel mixture. But the CSV feed line is pressurized all the time, whether the CSV is actuated or not, so if it has a leak it will leak all the time. You also said you saw a spray of fuel under the car, which would suggest the fuel lines there, rather than in the engine compartment where the cold start components are.

    I recently replaced the pump output line on my 73.5, which carries 60+ psi. It was dated 1976. The PO and I were living on borrowed time.
    --Richard
    Early 911S Registry #2337

  6. #6
    Besides old fuel lines, the alcohol seems to shorten fuel line life. I've had it happen on my own cars and for some reason in both cases it was the same line, the return line right where it clamps onto the steel line from the bulkhead just above the trans mount. In my case I had replaced that line only a few years previous, the fuel would ooze right through the fuel hose like a wet sponge. It was always the same line in the same location. It has nothing to do with the starting procedure. Sometimes a leak will occur at the fuel pump if the o-rings have dried up from non-use, then will stop leaking as the car is used and the seals swell up again.
    Early S Registry member #90
    R Gruppe member #138
    Fort Worth Tx.

  7. #7
    Member #2634 Mac911's Avatar
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    We tightened all the fuel and vaccum lines today. We could not get it to leak gas again. So maybe it was a loose gas line or if it was a vacuum line as Chris suggested hopefully we got it. I drive my car on a weekly basis so it would be odd for the o ring to be dry so quickly on the fuel pump. Thanks for all the input.

  8. #8
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    I hope it is fixed, but I recommend you replace all of the rubber lines, even up front by the fuel tank. Realize, if there is a fire the, 73.5 has no safety features to shut off the fuel pump. Gas will continue to flow at 70 psi till the key is turned off.
    Also, the engine and transmission are magnesium. Magnesium can burn, and it does so at such a high temperature that firefighters will not be able to extinguish it. It can only be stopped by smothering it with sand.
    E Sully
    1973.5 911T

  9. #9
    Two things. First, as mentioned above, the hand throttle simply pushes on a little barrel attached to the throttle pedal rod itself. It just pulls the rod a little bit. It is not separately attached to anything else.

    Second, that fuel pump can definitely fail or have problems at any time. This is not the same issue. But, my 73.5 fuel pump failed at 65 mph after 170,000 miles.

  10. #10
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    Another Point 5 chiming in here. I know the scary feeling of a gas smell and not fun when 10 miles away from home, pop the lid and see gas spraying from an olden rubber line. Lessons learnt. After 25 years of stewardship of a 73.5T I replace ALL the rubber fuel lines every three years, ready or not! Peace of mind and drive it.
    I pressed the pedal on a warm engine and it sprayed fuel in the air box and then got the BANG. Pop-off valve dislodged needing to be pushed back in. Lucky to drive it home, I guess. Sensitive beast has a few rare moments.

    Cheers,

    Jeff
    1973.5 911T
    S Registry #1977
    Point 5 Registry #1

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