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  • Holley carb problems

    New and frustrated. 79cj7 258 with Holley carb. My jeep starts and idles excellent but as soon as I hit the gas the jeep falls on its face. Experiencing intake backfire as well as exaust backfire. Timing is correct. Vacuum is good. Coil is good. I've changed the plugs, wires, cap, rotor etc.... Every adjustment on the carb I make seems to have no effect on the situation. Any suggestions? thanks.

  • #2
    Quite possibly a worn cam. if one (or more) lobes are worn, the valves are not opening enough to get rid of the spent exhaust out of the cylinder. Its easy to check for worn lobes, just pull the valve cover and look at the valve rockers while the engine is running... they should be moving top to bottom about 3/8" and should all be uniform. If one or more is not rising the same as the rest there is your problem.
    Are you back firing through the carb on excelleration??

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    • #3
      back fire

      There always seems to be a small backfire. Even at idle. But if I give it too much gas at once, everything seems to stop for a moment, dies sometimes, but sometimes the engine will recover after the brief moment and rev up. From idle, the only way to get the jeep moving is to ease very slowly into acceleration.

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      • #4
        try rejetting it

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        • #5
          More info on the holley carb problem.

          79 cj7 258 holley carb.Carb retarded. I was messing with the carb earlier and I closed the choke plate nearly all the way because I've tried just about everything else. The rpm jumped to about 1500 and from there I could hit the throttle as fast as I could with no stop n stutter action. Could this be a clue as to what the problem is? See earlier post for original problem. thanks

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          • #6
            Not being familiar with the 258 carb , is your vacum advance running off of ported vacum ?( bad vacum advance module ).

            Accelerator pump adjustment correct ?

            Tweak the distributor a little at a time , to see if you can work the stumble out of it .

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            • #7
              intake & Carb gaskets sealing tip

              Sometimes if the intake or Carb gaskets aren't sealing correctly you can get
              similar symptoms ,, to check the seals I'll use a rattle can of starter fluid with a straw and spray over the seals whlie the engine is running,, if there is a leak the starter fluid will be sucked in and the engine will speed up some,, Caution though starter fluid highly flamable


              Kelse

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              • #8
                This may sound silly, but it cured mine.

                Tighten the alternator a bit more. My belt was only a tiny bit loose, wasn't even squealing. We tightened up the belt and it was just fine.

                Hope its that simple for ya.

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                • #9
                  I know what and where the accelerator pump is but I don't know the procedure for adjusting it.
                  I've move the distributor in every position possible.
                  I'm pretty sure the advance is working but it never hurts to check again. thanks for the help.

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                  • #10
                    What size Holley are you running on that 258? It may be too big. Closing the choke just puts the curb idle up on a cam to increase the RPM when cold. This is as it should be but...

                    Choking the engine also cuts down on the CFM which may indicate too big of carb. But it also get's you past the transition ports and puts you into the main fuel circuit in the Holley so maybe a: your accelerator pump is not working b: Your your power valve is not working correctly.

                    What ignition are you running? Stock? I would go with an upgrade as soon as possible. No carb adjustment in the world is going to help you if you have a weak spark. 79 uses a DuraSpark so a simple TFI upgrade would help tremendusly. Basically your just putting on a better coil with a bigger distributor cap to handle the increase voltage to jump the bigger gap in the plugs.

                    Back to the carb, What are you adjusting? Just the idle jets? they should only effect the idle.

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                    • #11
                      I've been adjusting the float level, acc pump, idle screw, and mixture screws. This carb came off a 86 258 manual.( I have an automatic, hate it, would this affect it?) I am running stock coil and distributor. I'll try and figure out if the other jeep had any upgrades. I think it may have had an electric fuel pump but not positive. And now that I think of it...the other jeep came from colorado so it might need some different guts for Indiana.

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                      • #12
                        Originally posted by jessetango
                        .... And now that I think of it...the other jeep came from colorado so it might need some different guts for Indiana.
                        Good thought. Check the jet size.

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                        • #13
                          Originally posted by fuzz401
                          try rejetting it
                          yogi beara...

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                          • #14
                            Holley Carb Jet Question

                            79CJ7 258 AUTO 4412-3 HOLLEY CARB. I've come to the conclusion that I need to rejet the carb. It was installed on a 258 in Colorado. I live in Indiana. The factory jet size is 70. The jets currently in the carb are 73 causing the engine to run lean. Would this have a MAJOR affect on the performance. Don't want to but an entire set right off the bat. But afraid that the stock jet # might not be what I need. Any suggestions?

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                            • #15
                              I would only get a couple size jets 74-75-76 and some gaskets for the carb put a vac gage on the unported port and see what vac you have cut that in 1/2 and put a power valve in that size - 14 vac put in a 7.0 power valve and go up 1 size in jets and keep working on it till you get there
                              it can be hard some times to tell what is to rich or lean by the stumbel
                              did you addjust the accel pump cam there are 2 screw holes for it try the other hole first

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