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What is the correct ignition timing for an ’87 GMC Caballero with a vacuum distributor?

That is a trick question. No one could answer that question. The ’87 Caballero didn’t come with a vacuum distributor. It came with a computer controlled distributor. However, if you were to retrofit it with a vacuum advance distributor for $55 off ebay, the correct ignition timing would be 10 degrees before top dead center:


  1. Darby 06/02/2019

    Oh! Look! A carburetor!

  2. Fishwrapper 06/02/2019

    How is it that you tagged this as “off topic?” It’s no more random than some of the shinola the Trustees come up with…

  3. Deplorable Duck 06/02/2019

    I’m guessing that the number of owners who have a distributor and have touched it is way under one percent at this point. If there’s ever an EMP, you’re all set…

    • uomatters Post author | 06/03/2019

      Full disclosure: I’m no foil hatter – this new distributor is still Hall effect. I’ve spent enough of my life adjusting VW points. But the timing advance is controlled by weights, springs, and vacuum rather than by the first gen GM ECU computer. I did this because some previous owner had replaced the original Quadrajet E4ME carb with an earlier purely mechanical version. This meant the ECU was not getting any input from the carb on throttle position, nor giving it any input on fuel metering. So near as I can tell the ECU was controlling the advance based purely on engine temp and exhaust oxygen. It ran for shit.

      A rebuilt E4ME was $279 – and no certainty how long the ECU would last – so instead I went with the $55 mechanical/vacuum advance carburetor. Runs great, and should be better off the line once I get the vacuum line hooked up to the carb. I believe the ECU is now irrelevant, and I plan to test this empirically next weekend.

      My goal is 16 mpg on the highway at 85, and enough acceleration to beat Glen’s ’76 BMW 2002 in the 1/4 mile. I’m willing to put a 350 in it if that’s what it will need.

      And if Gov. Brown ever passes her carbon trading bill, I will happily pay the extra 10 cents a gallon to some corporate pirate for carbon offsets. Anyone know where I can get the AC’s R-12 recycled? I don’t want to vent that into the ozone.

      • CSN 06/03/2019

        Where’s your quarter-mile test track? I know a good salt flat in the Nevada desert….

      • just different 06/03/2019

        A 350?? 16 mpg??? This makes me think that the price of gasoline should vary with the weight of the vehicle, say $2/gallon/ton.

    • A duck 06/03/2019

      Deplorable Duck…EMP? We’ll ALL be on the bike share program!

    • darby 06/06/2019

      I have, and have had in the past, many an automobile motor with a distributor and not only have touched them, but have replaced them.

      I wonder how many faculty, besides our esteemed uomatters fella, even knows what it is that the car motor distributor function might be.

      Anyone else know what points and are and why/how one might adjust their gap?

      • Fishwrapper 06/07/2019

        Or why and how to do so quickly for one’s overloaded 1970 VW Type II in a chain-up pulloff going over the Continental Divide…?

  4. Anonymous 06/04/2019

    Great My Cousin Vinny reference.

  5. Dog 06/07/2019

    hey all you gearheads

    I had a 1956 willys that exploded in to fire
    at 11,000 feet in the San Juan Mountains
    on my way to a ghost town called Carson

    gap separation and points didn’t seem
    to matter much in that case. The Willy’s
    Carcas is still there …

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