On-Car Q-jet Tuning Suggestions? - NCRS Discussion Boards

On-Car Q-jet Tuning Suggestions?

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  • Patrick H.
    Beyond Control Poster
    • December 1, 1989
    • 11608

    On-Car Q-jet Tuning Suggestions?

    Hello All,

    Well, I had the Q-doorstop-Jet adjusted as per earlier suggestions, and the choke et al are doing very well. I have one small question that I was hoping someone could answer.

    When releasing the accelerator pedal at a slow to moderate rate after having used all 4 bbl of capability, and the rear of the carb closes (i.e. air valve shuts, and I assume rods drop back into resting position), the car will seem to surge slightly, or actually INCREASE slightly in revs.

    Does this, in your best guess indicate a LEAN or a RICH condition? And at full throttle, or partial? In other words, am I too lean at full, thus I momentarily get "more" power when decreasing the air supply when backing off and closing the rear "barrels"? Or is there some other condition causing this slight surge?

    I am just wondering whether I need to adjust primary or secondary settings, and how. Otherwise the "doorstop" has, for some strange reason, been running quite well. And this, of course, is only a minor annoyance.

    Patrick Hulst
    Vice-Chairman (West), Michigan Chapter NCRS
    71 "deer modified" coupe
    72 5-Star Bowtie / Duntov coupe. https://www.flickr.com/photos/124695...57649252735124
    2008 coupe
    Available stickers: Engine suffix code, exhaust tips & mufflers, shocks, AIR diverter valve broadcast code.
  • Bill Clupper

    #2
    Re: On-Car Q-jet Tuning Suggestions?

    I'm sorry Patrick, but I forget the specifics of your setup, what year/engine are you running, full smog equipment in place? Probably some other things i'm forgetting, but the year of the car and the smog setup for that year come in to play. Generally, stock settings tend to the lean side in the early 70's, less so 68, '69 worse than '68 etc...

    Comment

    • Bill Clupper

      #3
      Re: On-Car Q-jet Tuning Suggestions?

      I'm sorry Patrick, but I forget the specifics of your setup, what year/engine are you running, full smog equipment in place? Probably some other things i'm forgetting, but the year of the car and the smog setup for that year come in to play. Generally, stock settings tend to the lean side in the early 70's, less so 68, '69 worse than '68 etc...

      Comment

      • Patrick H.
        Beyond Control Poster
        • December 1, 1989
        • 11608

        #4
        Re: On-Car Q-jet Tuning Suggestions?

        Bill,

        I post is so much I figured everyone knew.

        71 350/270 with 2.02/1.60 valves, 212/224 duration cam with .442/465 lift. Right now I have 73/41 primary jets/rods, and I believe DA secondaries. No smogs, cuz Zora left them off!

        Externally a very correct appearing motor, with just the few minor internal changes as above.

        Patrick
        Vice-Chairman (West), Michigan Chapter NCRS
        71 "deer modified" coupe
        72 5-Star Bowtie / Duntov coupe. https://www.flickr.com/photos/124695...57649252735124
        2008 coupe
        Available stickers: Engine suffix code, exhaust tips & mufflers, shocks, AIR diverter valve broadcast code.

        Comment

        • Patrick H.
          Beyond Control Poster
          • December 1, 1989
          • 11608

          #5
          Re: On-Car Q-jet Tuning Suggestions?

          Bill,

          I post is so much I figured everyone knew.

          71 350/270 with 2.02/1.60 valves, 212/224 duration cam with .442/465 lift. Right now I have 73/41 primary jets/rods, and I believe DA secondaries. No smogs, cuz Zora left them off!

          Externally a very correct appearing motor, with just the few minor internal changes as above.

          Patrick
          Vice-Chairman (West), Michigan Chapter NCRS
          71 "deer modified" coupe
          72 5-Star Bowtie / Duntov coupe. https://www.flickr.com/photos/124695...57649252735124
          2008 coupe
          Available stickers: Engine suffix code, exhaust tips & mufflers, shocks, AIR diverter valve broadcast code.

          Comment

          • Bill Clupper

            #6
            Re: On-Car Q-jet Tuning Suggestions?

            Patrick, when I had a new '74 , I was upset with the performance & I replicated the jetting from a '67 396-350hp engine and it ran like a rabbit. got approx 20 mpg on the highway also. Just a note, keep the secondary "flapper" valve spring more to the "tight" rather than the "loose" side. Also, remember to optimize the distributor curve. The '65 -365 hp curve is a good one to mimic.

            Comment

            • Bill Clupper

              #7
              Re: On-Car Q-jet Tuning Suggestions?

              Patrick, when I had a new '74 , I was upset with the performance & I replicated the jetting from a '67 396-350hp engine and it ran like a rabbit. got approx 20 mpg on the highway also. Just a note, keep the secondary "flapper" valve spring more to the "tight" rather than the "loose" side. Also, remember to optimize the distributor curve. The '65 -365 hp curve is a good one to mimic.

              Comment

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