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  • Popping Through Carb

    So the other day I was driving the GMC and it started sounding like I had a really bad exhaust leak and the transmission started holding gear higher in the rpm range before the shift. well today I got time to investigate and the exhaust is all good, but when I start the truck and it's idling it starts popping real loud though the Carb. And it's not backfiring, I mean no flames are shooting out, but there is a loud popping noise coming from the carb. I checked timing it is holding rock solid at idle. So what do you guys think it might be??
    The Green Machine.
    http://s1.postimg.org/40t9i583j/mytruck.jpg

  • #2
    Sounds like an Exhaust valve is not opening. Either Rocker is off the pushrod or the cam is flat.
    If you can figure out which cyl is missing take the valve cover off on that side and take a look
    Assuming the spark plug wires are not crossed
    Last edited by wrenchn2; July 31, 2017, 06:15 PM.

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    • #3
      Originally posted by wrenchn2 View Post
      Sounds like an Exhaust valve is not opening. Either Rocker is off the pushrod or the cam is flat.
      If you can figure out which cyl is missing take the valve cover off on that side and take a look
      Assuming the spark plug wires are not crossed
      Wires are fine it was running fine and then all of a sudden it started doing this.
      The Green Machine.
      http://s1.postimg.org/40t9i583j/mytruck.jpg

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      • #4
        Popped the valve cover off and looky what I found.... Thanks for the direction....
        The Green Machine.
        http://s1.postimg.org/40t9i583j/mytruck.jpg

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        • #5
          Oh the glory, it had a friend... Looks like I need to check rocker geometry.....
          The Green Machine.
          http://s1.postimg.org/40t9i583j/mytruck.jpg

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          • #6
            Bummer on the broke parts, BS for the win!
            http://www.bangshift.com/forum/forum...-consolidation
            1.54, 7.31 @ 94.14, 11.43 @ 118.95

            PB 60' 1.49
            ​​​​​​

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            • #7
              so it bent a pushrod first and broke the guide? Dont see a bunch of rubbing on them.

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              • #8
                Hmmm I don't know what would cause that. Glad you found it.

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                • #9
                  I am impressed! I have never experienced that symptom so now hopefully I can remember it should I encounter it in the future.

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                  • #10
                    Originally posted by anotheridiot View Post
                    so it bent a pushrod first and broke the guide? Dont see a bunch of rubbing on them.
                    I still need to pull the pushrod, I started replacing them with new ones from Comp, but had to leave before I got to the broken ones... For the record the ones that broke were from Manley.....
                    Last edited by BigAL; August 2, 2017, 07:14 PM.
                    The Green Machine.
                    http://s1.postimg.org/40t9i583j/mytruck.jpg

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                    • #11
                      And I had problems with comp! Good luck. I think quality control has been thrown out with the dish water.
                      Pt 2010, Long Haul 2011,12,13,14,15,16,17, 18, 19, 23
                      If you wait, all that happens is that you get older

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                      • #12
                        Originally posted by corvettedad View Post
                        And I had problems with comp! Good luck. I think quality control has been thrown out with the dish water.
                        I will say these are like 20 year old Manley pushrod guides, though they were still new, just had them all this time and decided to use them on this motor. The two that I pulled today looked fine, so we'll see tomorrow what's going on with the ones that broke...
                        Last edited by BigAL; August 3, 2017, 12:19 AM.
                        The Green Machine.
                        http://s1.postimg.org/40t9i583j/mytruck.jpg

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                        • #13
                          Took off the passenger side valve cover to check the other side and low and behold, #6 and #8 had the same thing happen to them, it's odd that both the back cylinders on both sides would do the same thing.... I got a pushrod angle checker and everything checks out, so I have the correct length pushrods, so I'm not sure what to chalk this one up to.... Anyway got the new pushrod guides installed and just need to adjust the valves and button her back up and I'll be good to go....
                          Last edited by BigAL; August 5, 2017, 12:41 PM.
                          The Green Machine.
                          http://s1.postimg.org/40t9i583j/mytruck.jpg

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                          • #14
                            Did you happen to notice if the rocker studs are pressing down tight on the pushrod guides.
                            Since so many broke I am wondering if something is wonky there. One of those had marks on the bottom where it looks like it was against the head.
                            They may not be sitting flat under the stud and rocking back and forth.
                            I don't think bad metallurgy was the cause. But anything is possible.

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                            • #15
                              Originally posted by wrenchn2 View Post
                              Did you happen to notice if the rocker studs are pressing down tight on the pushrod guides.
                              Since so many broke I am wondering if something is wonky there. One of those had marks on the bottom where it looks like it was against the head.
                              They may not be sitting flat under the stud and rocking back and forth.
                              I don't think bad metallurgy was the cause. But anything is possible.
                              That mark is probably from when it broke off and wedged against the head the pushrod, even broken it was kind of still doing its job...

                              Funny thing is everything in the valve train is Comp, except those guide plates, they were Manley, maybe there is something to using all one manufacturers parts, instead of mismatching....
                              The Green Machine.
                              http://s1.postimg.org/40t9i583j/mytruck.jpg

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