Distributor & vaccume question

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by rustypig, May 7, 2001.

  1. rustypig

    rustypig Registered Member

    May 7, 2001
    Likes Received:
    Suisun CA
    On my 78 Blazer, the original owner yanked all the emissions crap off (kewl), and was running the distributor directly off of a carb vaccume. I believeon the original setup it pulled vac from the ported vaccume switch in the thermostat cap. The main problem I'm having is that it feels like my timing is not right....NO POWER on accelleration. The timing is set right w/ vac line disconnected and capped, but I'm thinking that when I reconnect it for normal operation it is automatically advancing the timing. Anyway this thing should be "getting it" and it's not (only 20k on engine, rv cam, new carb, edelbrock intake, headers, and I ported and polished the heads). The thing runs great, but feels like I got the e-brake on when I drive..ANY idea's are appreciated.
  2. dyeager535

    dyeager535 1 ton status Premium Member

    Dec 13, 2000
    Likes Received:
    Roy WA
    Well, in most cases, vac advance needs to be hooked up to "ported" vacuum, which is typically one of the smaller ports on teh drivers front side of the Q-jet. Easy to test, at curb idle (in other words low idle) the port you are interested in should not "leak" if it is unplugged. But as you get more into the throttle, you will feel the "suck" on your finger. Thats the one you need.

    Vac advance, in reality, is not a major factor in acceleration...it advances spark under part throttle (read:cruising) but under moderate to heavy acceleration, since there IS no vacuum, or very very little, the vac advance does nothing, and mechanical advance is doing the work.

    Vac advance is basically an MPG tool.

    My K5 and Chev/Olds tech/links page: <A target="_blank" HREF=http://www.dorianyeager.com/index2.html>http://www.dorianyeager.com/index2.html</A>

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