Engine dieseling and stop idle solenoids

Discussion in 'Troubleshooting & Diagnosis' started by Tphil413, Nov 23, 2017.

  1. Tphil413

    Tphil413 Veteran Member

    Jun 1, 2007
    San Francisco, CA
    My '71 has had an ongoing problem with engine dieseling. In the past I've set the engine idle very low and turned the car off in gear. This works most of the time but I still see some dieseling. I was researching dieseling and saw some discussion about factory stop idle solenoids to help this problem. I found the Edelbrock solenoid 8059 that seems like the same thing as the factory stop idle, but all the descriptions say its for use with factory AC to bump the idle under load. Is anyone running this solenoid to help with dieseling? I'm running an Edelbrock 1806 650 AVS Thunder carb with electric choke. Sounds fairly easy to set up, but the part is a bit pricey.
  2. larrylarry

    larrylarry Veteran Member

    Dec 22, 2011
    San Antonio Tx
    If its dieseling your timing is to retarded. Those solenoids were to bump up the idle when the A\C is being used. With your engine fully warmed up the idle should be around 800-900 rpms. Timing should be 36-34 degs. Bet you're timing is about 45 degs.or more. Get the timing set first then adjust the idle.
  3. Tphil413

    Tphil413 Veteran Member

    Jun 1, 2007
    San Francisco, CA
    Timing is set at 12° initial and 25° mechanical. Fully warmed up in gear idle set at 650 rpm. In the past I needed to drop idle down to around 550 rpm before I could turn it off in gear without it dieseling. That's tough because at that low idle I only have around 5 lbs of vacuum in gear. Hoping an idle stop solenoid might allow be to keep my idle closer to 650 without dieseling.
  4. McCune

    McCune Veteran Member

    Aug 22, 2015
    st.george utah
    Then why does that 979 mile 74 non A/C Z28 have a anti diesel solenoid on the carb?
  5. Tphil413

    Tphil413 Veteran Member

    Jun 1, 2007
    San Francisco, CA
    Yeah that was my question too. Maybe these solenoids can be set up to handle AC or dieseling issues. I'd just feel better if someone in the forum has run this setup and seen it work before I drop $165 at Summit Racing.
  6. Gary S

    Gary S Administrator Lifetime Gold Member

    Apr 14, 1999
    Bismarck, North Dakota
    Those solenoids can be set up to do either job. They can handle the additional A/C load or they can be there to drop the idle when the engine is shut off so it doesn't diesel. The main cause of dieseling is poor gas. If the gas has high enough octane, you can adjust the carb correctly and it should work. The timing needs to be advanced enough so it idles fast enough that the carb can be set down far enough so the primary is closed and the engine is idling only on the idle circuit. If the primary is partially open, it feeds enough fuel at shutoff to make the engine diesel.
    But, you can't advance timing if you have poor fuel because that will cause detonation which can kill the engine.
  7. twozs

    twozs Veteran Member

    Aug 5, 1999
    hopewell jct ny
    I've been saying this for how long ?

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