Questions for you Q-jet EXPERTS please!

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by Ben Malinski, Dec 10, 2002.

  1. Ben Malinski

    Ben Malinski Guest

    I have no smog control devices on my truck! (Lucky to be in Korea I suppose!) No EGR, canisters, etc...
    The only line I have hooked up is the vaccum line from the distributor and one for the choke pull off. Where does the line go from the distributor? Passenger side or drivers side front port? I have set the timming, disconnected and plugged the line of course, and notice no difference in the timming mark. Seems to run the same. Connecting the line to either side of the carb also yields no difference. Is this "normal?" I read about full vacuum or manifold vacuum, yet again, I notice no difference. Both of the ports on this Q-jet seem to be aligned with each other at each corner of the carb. I'll pull the hose and connect it back and forth trying to find some difference in driving and agin, notice nothing. Opinions, suggestions?
    Happy Holidays all from Korea! You are all lucky to be with your families! It's FREEZING over here! Below zero!
  2. Blazer1970

    Blazer1970 1/2 ton status

    Feb 17, 2000
    Likes Received:
    Old Mission, MI
    There are a lot of differences between various Q-Jets on how the vacuum ports are designed. There are manifold vacuum ports, and there are various types of ported vacuum. Some ported vacuum ports are set-up for vacuum advance, some are set-up for EGR, and some were used for other stuff. The best way to decipher this is to use a vacuum gauge. Hook it up to each port, and note what kind of vacuum you see on that port as you go from throttle closed to full open. Also note that this behaviour will not be the same when the engine is under load as it is when you are sitting in the driveway. If you don't have a gauge, you can tell a lot just by holding your finger over the port while actuating the throttle. Is the diaphragm good in the vacuum advance actuator on the distributor? You can tell by hooking a hose up to it and sucking on the hose. If you can suck air through it, the diaphragm is bad. If the diaphragm is good, it sounds like all of the ports you are playing with are ported vacuum of some type, or you would see a difference in idle when the distributor is connected to them.

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