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Thread: Hot no start mechanical injection problem

  1. #1

    Hot no start mechanical injection problem

    I have 3 mechanical injection cars and I have a problem with one of them not starting after sitting for 15 minutes or so after shut down. This one happens to be a 1973 if that matters, others are 70 and 72. I have read through the only thread I can find,, that somewhat deals with my issue. It has a 964 part number ignition switch, pump recently rebuilt by pacific fuel injection, sound motor and starts and runs very well as if it doesn't have any problem when cold and warm as long as it doesn't need to be restarted. If I squirt a little fuel down stacks when it doesn't start it will fire right up so it seems like it heat soaks injectors and lines and needs extra fuel. Neither of my other cars running the same fuel have these issues. The kicker is if I use a remote starter and start from rear of car it will start right up. To me with this it seems like an electrical issue but I don't know why. Anyone have any direction they can point me in?

  2. #2
    I guess you already try to start with the pedal fully down ?

  3. #3
    Yes I have, the unusual part is I don't touch the pedal when using the remote starter and it still starts right up.

  4. #4
    Mine is also a little bit tricky to start when hot...just to be sure, did you check that ?

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  5. #5
    This sounds like a voltage drop problem. When you use a remote you're shortening the circuit path. You have a weak battery, high resistance starter or poor ground. Get battery load tested and if good install SR68X starter.
    Early S Registry member #90
    R Gruppe member #138
    Fort Worth Tx.

  6. #6
    I'll have to check the fuel plumbing, that hadn't entered my thinking process. The batteries were new last year and it spins so fast that voltage drop doesn't seem likely. I suspect the ignition switch was replaced looking for that issue. Its just strange that either adding a squirt of fuel it starts with the key or using the remote starter it starts after sitting and becoming heat soaked.

  7. #7
    If your battery and starter are okay then manually activate the cold start valve and crank the engine. See if that makes it start.
    Early S Registry member #90
    R Gruppe member #138
    Fort Worth Tx.

  8. #8
    Senior Member
    Join Date
    May 2006
    I had this problem on a '70E I restored. It turned out to be a sticky check (overflow) valve on the fuel filter console. The faulty valve would allow the system to depressurize and then the fuel in the lines and injectors would vaporize due to heat soak from the engine. Classic vapor lock. A new valve solved the problem.
    Last edited by tom1394racing; 06-19-2023 at 02:20 PM.
    Tom Butler
    1973 RSR Clone
    1970 911E
    914-6 GT Clone in Progress

  9. #9
    Thanks for all the replies. I will get to this in the next day or two and report back. Hopefully with a solution.

  10. #10
    Senior Member
    Join Date
    Nov 2003
    Santa Monica CA
    I used to have a problem where after a long drive in warm conditions; after the car was sitting for a couple of hours, was hard to start. This is a 1970 MFI 911S. Something to do with the original starter motors on 1970 cars. the .75 HP motors were not the best. so when I rebuilt the engine, I installed a "high torque" starter motor. It is the Bosch 1.5 HP motor used after 1972 911's Seems to be working fine now. Chris
    1. Chris-Early S Registry#205
    2. '70 911S Tangerine
    3. '68 911L Euro Ossi Blue

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