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Thread: 75 911S CIS help

  1. 12-03-2017, 06:57 AM #1
    jfd
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    75 911S CIS help

    Car won't start. Repeated attempts result in backfire. Blowoff valve bolwn off. Fuel pump works. Ran fine last time run. Recently replaced injectors.
    Probst Troubleshooting guide suggests cold start enrichment valve or thermo time switch may cause this? My factory manual is 1973 and doesn't seem to match the 75 S K basic CIS?
    Any help, suggestions, diagrams etc. is appreciated
    Thanks jfd
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  2. 12-03-2017, 07:13 AM #2
    Rick Cabell
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    Post says "blow off valve blown off". If that's the case, then your car won't start because you have no vacuum, to lift the sensor plate.
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  3. 12-03-2017, 07:40 AM #3
    jfd
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    75 911s cis help

    Quote Originally Posted by Rick Cabell View Post
    Post says "blow off valve blown off". If that's the case, then your car won't start because you have no vacuum, to lift the sensor plate.
    Thanks Rick. What made it blow?
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  4. 12-03-2017, 07:56 AM #4
    beh911
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    A backfire through the intake
    1969 S Coupe #761
    Early S Registry #1624
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  5. 12-03-2017, 08:50 AM #5
    72targa
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    http://www.pelicanparts.com/techarti..._off_valve.htm
    Peter Kane

    '72 911S Targa
    Message Board Co-Moderator - Early 911S Registry #100
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  6. 12-03-2017, 12:15 PM #6
    Frank Beck
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    Is this a trick?


    Be glad you have the tiny toilet seat otherwise I would have to sell you a new air box which I have several of.

    Glue it back in and check your mixture.
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  7. 12-03-2017, 04:00 PM #7
    jfd
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    Thanks guys
    Not a trick. Just never had it happen before and trying to find out why it happened. Thanks for the tips
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  8. 12-03-2017, 04:15 PM #8
    Jsottile
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    Start here http://jimsbasementworkshop.com/CIS/

    Could be anything based on your description.
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  9. 12-04-2017, 07:01 AM #9
    jfd
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    Thanks Jsottile
    Very informative site
    jfd
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  10. 12-04-2017, 07:13 AM #10
    dporsche74
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    grounded/damaged plug wire.. crank crank crank turn key off loud backfire common with the CIS..

    also if the fuel reg is shot and not holding pressure it will never start either.. good luck CIS is more fun then MFI
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