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What do you set your timing to?

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  • What do you set your timing to?

    I'm setting the timing on my 4.2L 84 CJ-7, with the Weber carb, and I was interested in what most people set their timing to? I've heard 4-8 BTDC, quite a large range I think. Anyone wanna help me narrow it down? Thanks.
    06 LJ: 3\" body lift, 33\" Mickey Thompson MTX\'s, a lot more soon to come

  • #2
    Get a vaccuum gauge, they are very cheap, and set it by that. Since no engine is identical, the best way to set it is for max vaccuum @ idle.

    Find a manifold vaccuum source, plug into that line with the vaccuum gauge and adjust timing so that maximum manifold vaccuum is achieved.

    Then go and adjust your carb idle mixture screws with the gauge still plugged in. Adjust one at a time to achieve max vac then lean it out VERY slightly.

    This is the best method to set timing and tune the carb.

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    • #3
      Chilton said 8 degeees for my 1990 4.2L with a carb.
      1990 YJ Sahara. <br />Half the lies I tell aren\'t true

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      • #4
        Lower than 8 seems really, really low. I'd aim for a base timing of 8-10. Remember to readjust the carb idle speed and idle mixture AFTER setting the timing.
        97 TJ Sport<br /><br />Artillery brings dignity to what would otherwise be just a brawl

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        • #5
          Where do you hook up the vacuum gauge? It's a 258 with the Weber...
          06 LJ: 3\" body lift, 33\" Mickey Thompson MTX\'s, a lot more soon to come

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          • #6
            I had an 88 yj 4.2 with the weber 32/36

            Like the above post said get a vacuum guage and attach to the front of the carb where the hose goes over to your distributor. I set my timing at 9 deg. Then start tuning the mixture and idel until you get about 11 inches. This may vary based on the age of your engine and conditions, ect. You may have to test it and re-adjust the timing and try again. 7-10 degrees should be your limit. When tuning periodically bump the accelerator and verify vacuum.

            Now when I first did this my timing jumped all over the place. I had to perform the Nutter. Then the timing stayed stable. I tryied running at 8deg then 9 and finally 10. 9 was the best for my set up with no ping and good acceleration.

            Be patient and keep tweaking until you like it.
            Nothing is fool proof to a sufficiently talented Fool!

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            • #7
              No, you don't want to hook the gauge at that point. The line that goes from the carb to the dist. is ported vac which runs the vaccuum advance mechanism.

              You want a manifold vac source. I just used my brake booster line.

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              • #8
                Where's the brake booster line?
                06 LJ: 3\" body lift, 33\" Mickey Thompson MTX\'s, a lot more soon to come

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                • #9
                  I went ahead and did what you guys described above connecting the gauge to the tube running from the weber to the distributor. She runs a lot better, but I noticed there was not too much needle movement in the gauge when I was tweaking the timing. I did leave it where I found max vacuum, although the vacuum only moved about 3 or 4 inches below max with lower BTDC settings.
                  06 LJ: 3\" body lift, 33\" Mickey Thompson MTX\'s, a lot more soon to come

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                  • #10
                    Well you only want to back it off 1" after you find the max but if you can start it all right and not get any pinging then leave it alone.

                    If your getting vacuum at idle on the line going to your distributor it is on the wrong port or your idle is to high.

                    start tuning the mixture and idel until you get about 11 inches.
                    11" is way too low. You should be arounf 18-20 at idle ior start looking for some vacuum leak. at 11" the the BBD will start to richen the mixture because it thinks it's under load. This will give you terrible gas milage.

                    Mine is set at 9*. I tested the vacuum method and got the same reading. Make sure you drop your idle back down after you get things adjusted. It should idle arounf 700 -750 RPMs it everything is all right. To high and your not on the idle circuit anymore. You may get run-on or dieseling if your too high.
                    Resistance is useless,<br />Repeal Ohms Law.

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                    • #11
                      Thanks, it's running real strong, I think I need to back the idle down a bit, I have no tach, so I'm going by ear. This is the best she's run since I bought her 3 years ago!
                      06 LJ: 3\" body lift, 33\" Mickey Thompson MTX\'s, a lot more soon to come

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                      • #12
                        dillon is correct. The distributor line is ported vac and you need maifold vacuum. look for the line going to the heater control through the firewall. 8 degrees is probably fine. Remember too much advance will cause pinging under load .
                        1954 Willys Overland Wagon 88YJ with 4.0, AX-15, 2\"BDS SOA, Hi-Steer, 36\" Swampers, High Pinion D-44 and a Ford 9\" with 4.56s\'s, Locked F&R, AA SYE with custom HD Drive shafts, Motorcraft 2150, GM HEI, OBA system, Warn 8274, A LOUD air horn, and a hole in my wallet.

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                        • #13
                          If you have no idea about what we are talking about (manifold vs ported vac) grab a Haynes manual for your Jeep. It'll have a diagram showing which vacuum lines are what.

                          The whole point of ported vac is that it isn't around until RPM's are increased above a certain point. That's why it is used w/the distributors vac advance mechanism, it'll advance the timing when RPM's go up.

                          Manifold vac drops off as you increase the engine's RPM. It'll vary as engine speed changes or you decelerate, etc. A vac gauge is useful also beyond the tuning process for checking to see if you have misfires, stuck valves, etc. The vac gauge should have come with some sort of instructions either in the package or on the back. It'll tell you what needle movement is caused by.

                          Good luck and hope you get 'er running well. I was never really able to tune my 304 that well until I tried this method and it ran like a champ from then on out.

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                          • #14
                            You can also set the idle mixture by ear and or dash tach. Just adjust the mixture screws until you get the highest rpm out of the engine or highest rpm on the tach. You should be able to "earball" this by listening to the engine. If the idle speed ends up being too high after that, slightly adjust the fast idle screw to a acceptable rpm. You *may* have to readjust the mixture screws after doing that, so this may take a few times to get it right. The real cat's ass way to adjust a carb these days is to use a wideband O2 sensor hooked up to a air/fuel monitor....you can almost get fuel injection like air/fuel ratios that way.
                            97 TJ Sport<br /><br />Artillery brings dignity to what would otherwise be just a brawl

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                            • #15
                              Originally posted by dillonjm:
                              If you have no idea about what we are talking about (manifold vs ported vac) grab a Haynes manual for your Jeep. It'll have a diagram showing which vacuum lines are what.
                              I don't have a Jeep carb, I have the Weber. So the Hayne's wouldn't do much, and I have a Chilton's manual anyway. Is there anything wrong with leaving her how she is? She's pulling good and there's no ping...
                              06 LJ: 3\" body lift, 33\" Mickey Thompson MTX\'s, a lot more soon to come

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