Rebuilt CCC Qjet Tuning

Discussion in 'Engine Topic' started by MP81, Oct 8, 2019.

  1. MP81

    MP81 Veteran Member

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    Just rebuilt my E4ME Qjet using one of Cliff's rebuild kits (twice - I didn't adjust the float height or put the pull clip in the right spot the first time - wasn't something I found out about until after putting it back on the car), and was wondering if there is a good method to look at for tuning it.

    I set the lean mix screw to 3 1/2 turns out and the idle air bleed valve screw to 4 turns (I think), but didn't mess with the idle mix screws (though I think I did turn one the first time I put the carb on the car, when it ran like absolute poo - likely super rich due to the float being probably 1/4" too high).

    I have a dwell meter, and a piece of 16-gauge wire with a crimp terminal on the end in order to connect the dwell meter (which has a large alligator clip) to the diagnostic connector (which has the spade terminal enclosed in a way the alligator clip cannot attach), but when I first tried to check things, I'm not sure it was reading properly (I had it set to the 6-cylinder setting) - then again, the car was running so bad (it tried to keep running after I shut it off the first time), it wouldn't have been worth it anyway.

    That said, after fixing the float height, replacing the air-bleed o-rings and putting it back on, it runs better, but still not great. Sometimes the idle will drop really low...like 500 RPM or so (and then it throws a CEL, which disappears after you turn it off and try to read them). But when you rev it, it seems to enjoy that.

    What's the best way to go about getting this thing dialed in, as it sounds like that's where I'm at now (which makes sense). Letting it run for about 5 minutes should allow the dwell reading to show up, right? I think I am looking for 30 degrees of dwell, but I'm not sure which adjustments I should make (and in what order) to get there.

    Any help would be appreciated!

    Thanks!
     
  2. 1980RS

    1980RS Veteran Member

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    Wow, a C3 Q-jet. So is this the one with an MC solenoid on it? is so there are special tools that you need to get the setting right for the primary side. We used to rebuild them all the time, try to go for 35° as it runs fatter and better. I do have one of those Q-jets if yours does not work and I have a really nice H.O. 305 L69 Qjet without the choke, would let you have them both for a good deal if you find this one does not work out.
     
  3. MP81

    MP81 Veteran Member

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    C3? As in Corvette? It's the stock one to the car. But yes, has the MC solenoid and the TPS sensor.

    So I just went out there and inhaled a bunch of exhaust fumes (car is backed into the garage, so even with the door behind it open and the main garage door open, it still fills up pretty well with CO) and let the car run till it was up to temp.

    Prior to that, I also checked the passenger idle mix needle (which I never touched from what it was before), and it was four turns out. I changed the driver-side one (which I did mess with during the initial installation of the rebuilt carb) to match.

    I hooked up the dwell meter and...it read 3. That's all it would read. 3. It did not change if you increased the throttle at all...just, 3.

    Towards the end it started trying to idle lower, and the check engine light came on. Again, after turning off (with check engine still illuminated) and checking the code, all I got were just code 12s. So apparently there is one, but it doesn't want to show me.
     
  4. biker

    biker Veteran Member

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    No, C3 as in CCC I think? computer controlled carb.
     
  5. MP81

    MP81 Veteran Member

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    OH - C to the third power, got it. That makes more sense now!

    Must have been all those fumes.
     
  6. RickM

    RickM Veteran Member

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    Sounds like you don't have the rich stop and lean stop dialed in.

    You need to make sure that you have between 2/32 and 4/32 travel between them.

    You do this by putting a small ruler down one of the "D" holes next to the Idle Air Bleed Valve and measure the travel of the solenoid plunger.

    Very easy to do if you have the small ruler that comes with the CCC carb tools. I suspect you are off making the car run way too rich.

    Your carb rebuild kit may have this procedure if not you need find the info. Here is a short pic of what I am talking about.

    upload_2019-10-8_18-32-36.png

    Once you have this dialed in, after the car warms up and goes into closed loop (Reads Oxygen Sensor) the car should not run so rich.

    But you still need to get a varying dwell. You can tell if it is running too rich by creating a vacuum leak (remove a vac hose), this should change the dwell meter if it is not moving.
    OR
    If the car is running to lean put your hand over the carb like you are closing the choke this should change the dwell meter in the other direction.

    Once you deterimine that you are running too rich or too lean you can try adjusting the Idle adjustment screws in or out and then fine tune with the Idle Air Bleed valve.

    But you first have to get the 2/32-4/32 adjustment first.

    If you still cant get a varying dwell you will have to either move BOTH rich and lean stop adjustments the Same amount to either make the car run richer or leaner.

    It's really not this complicated once you understand what is going on.

    Hope this helps
    RIckM
     
  7. 1980RS

    1980RS Veteran Member

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    Another thing to make sure of is take the Mixture Control Solenoid off and check and make sure the rubber tip is not broken off.
     
  8. MP81

    MP81 Veteran Member

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    MCS was all good when I rebuilt the carb.

    I'll take a look and see if I can find that tool online to measure the movement there. Could I possibly use the vernier (depth) portion of my calipers to do the same measurement?

    So, all that aside, shouldn't I get some kind of change in dwell even as is? In my mind, it's almost like its not reading at all. It might be a little rich, but it's not that rich - not even close to how rich it was the first time I put it back on the car (prior to the float adjustment).
     
  9. RickM

    RickM Veteran Member

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    No until you get the oxygen sensor to say you are running lean the meter will stay pegged.

    That is why you should try to induce a vacuum leak that will make the car run lean. Then the O2 sensor will see a lean condition and the meter will swing in the other direction.
     
  10. MP81

    MP81 Veteran Member

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    But only when the engine is warm (thermostat opens), yes?
     

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