Rare 69 427 Vacuum Advance Anomaly for the Experts - NCRS Discussion Boards

Rare 69 427 Vacuum Advance Anomaly for the Experts

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  • Brad H.
    Expired
    • January 26, 2009
    • 250

    Rare 69 427 Vacuum Advance Anomaly for the Experts

    I'm hoping one of our engine gurus might comment on this crazy problem no one seems to have heard of. First, I'm not an amateur with older GM engines. I only mention this so that commenters can assume the basic stuff has been dealt with. The engine in question is an original to the car 69 L-36 427. The engine was rebuilt stock about 3000 miles ago. The distributor began to make a noise that sounded like something was hitting something inside and in fact a stethoscope confirmed this. The engine was also beginning to not run as smoothly as it had in the past. I decided to send the distributor to Dave Feidler of T.I. Specialty as I have used him before and respect his work. I also sent the Q-jet to Cliff Ruggles of Cliff's High Performance Q-Jets.
    Sure enough, Dave told me the distributor was a mess and that someone had really screwed it up during a past rebuild. Dave completely rebuilt it, replaced the vacuum advance and replaced the points with his single wire in the cap electronic ignition. Cliff also informed me that the carb was equally as screwed up but was able to bring it back.
    So this was the set up. Engine started right up and I timed it with the vacuum disconnected from the advance can. Engine runs pretty smoothly and all noise is gone from the distributor and there are no misses. I set the initial timing at 8 deg. Now here is the crazy part. When the vacuum hose which comes from the ported location at the carb is connected the engine immediately runs rough and has a subtle miss at idle and at steady state rpm around 2000 rpm. I tried changing the vacuum source from the carb to the direct vacuum port on the intake. No change. I tried rotating the distributor through it's range to change / reduce the advance. Absolutely nothing I tried would change this roughness. Finally, I have just plugged the vacuum off and I am now running the engine with the vacuum advance disconnected. Engine runs smooth and is smooth at all power settings. It does not seem to have the same power that it had previous to the distributor being re-worked and this may be due to the vacuun advance discnnected. I'm just out of ideas and have just about given up figuring this out.
    Hope someone has run across this craziness who might offer some suggestions.
    Thanks,
    Brad
  • Joe L.
    Beyond Control Poster
    • January 31, 1988
    • 43198

    #2
    Re: Rare 69 427 Vacuum Advance Anomoly for the Experts

    Originally posted by Brad Hood (49930)
    I'm hoping one of our engine gurus might comment on this crazy problem no one seems to have heard of. First, I'm not an amateur with older GM engines. I only mention this so that commenters can assume the basic stuff has been dealt with. The engine in question is an original to the car 69 L-36 427. The engine was rebuilt stock about 3000 miles ago. The distributor began to make a noise that sounded like something was hitting something inside and in fact a stethoscope confirmed this. The engine was also beginning to not run as smoothly as it had in the past. I decided to send the distributor to Dave Feidler of T.I. Specialty as I have used him before and respect his work. I also sent the Q-jet to Cliff Ruggles of Cliff's High Performance Q-Jets.
    Sure enough, Dave told me the distributor was a mess and that someone had really screwed it up during a past rebuild. Dave completely rebuilt it, replaced the vacuum advance and replaced the points with his single wire in the cap electronic ignition. Cliff also informed me that the carb was equally as screwed up but was able to bring it back.
    So this was the set up. Engine started right up and I timed it with the vacuum disconnected from the advance can. Engine runs pretty smoothly and all noise is gone from the distributor and there are no misses. I set the initial timing at 8 deg. Now here is the crazy part. When the vacuum hose which comes from the ported location at the carb is connected the engine immediately runs rough and has a subtle miss at idle and at steady state rpm around 2000 rpm. I tried changing the vacuum source from the carb to the direct vacuum port on the intake. No change. I tried rotating the distributor through it's range to change / reduce the advance. Absolutely nothing I tried would change this roughness. Finally, I have just plugged the vacuum off and I am now running the engine with the vacuum advance disconnected. Engine runs smooth and is smooth at all power settings. It does not seem to have the same power that it had previous to the distributor being re-worked and this may be due to the vacuun advance discnnected. I'm just out of ideas and have just about given up figuring this out.
    Hope someone has run across this craziness who might offer some suggestions.
    Thanks,
    Brad

    Brad-------


    How does the engine run with the vacuum advance disconnected and the vacuum port at the carburetor not plugged off? If it's about the same as with the vacuum advance connected, I'd say the diaphragm in the vacuum advance has failed and is creating a vacuum leak.
    In Appreciation of John Hinckley

    Comment

    • Stuart F.
      Expired
      • August 31, 1996
      • 4676

      #3
      Re: Rare 69 427 Vacuum Advance Anomoly for the Experts

      Could it be that the advance plate is tipping? What do your expert rebuilders suggest?

      Stu Fox

      Comment

      • Brad H.
        Expired
        • January 26, 2009
        • 250

        #4
        Re: Rare 69 427 Vacuum Advance Anomoly for the Experts

        Joe,
        Good idea but I did think of that.
        Thanks!
        Brad

        Comment

        • Brad H.
          Expired
          • January 26, 2009
          • 250

          #5
          Re: Rare 69 427 Vacuum Advance Anomoly for the Experts

          Thanks Stuart,
          I have wondered about that but was not sure how to prove it out short of pulling the distributor. Dave ran the distributor on his machine and set up it's optimum spring tension and checked it's operation. I would have thought that if the plate was tipping that it would have shown up on the machine. The distributor is such a pain to get out with all the shielding and wires involved so I was hoping to get as much feedback as possible before I yank it back out. I can't imagine where else the problem may be other than the distributor though....
          I'm grateful for any ideas out there.
          Brad

          Comment

          • Gene M.
            Extremely Frequent Poster
            • March 31, 1985
            • 4232

            #6
            Re: Rare 69 427 Vacuum Advance Anomoly for the Experts

            Brad
            It is simple to put a vacuum gage in line with the distributer can to verify no leaking.

            Use another known good distributer to see if problem persist.

            Pulling distributer a pain? Can't be much simpler. It's not like changing the clutch.........

            Comment

            • Michael W.
              Expired
              • March 31, 1997
              • 4290

              #7
              Re: Rare 69 427 Vacuum Advance Anomoly for the Experts

              Originally posted by Brad Hood (49930)
              When the vacuum hose which comes from the ported location at the carb is connected the engine immediately runs rough and has a subtle miss at idle and at steady state rpm around 2000 rpm.
              What happens to the timing when you connect the advance canister to the ported carb connection?

              Comment

              • Brad H.
                Expired
                • January 26, 2009
                • 250

                #8
                Re: Rare 69 427 Vacuum Advance Anomoly for the Experts

                There are certainly things much more of a pain than pulling the distributor. I wanted to get some ideas before I pull it for no reason if something else might be the culprit. As I wrote, there is no difference whether the ported vacuum port is used or straight manifold vacuum. With the ported vacuum port selected, and the engine is at idle there is no vacuum to the advance can so no abnormal condition results. When the throttle is brought up then ported vacuum is introduced and the roughness ensues. If straight manifold vacuum is used for the advance can the rough engine/miss is continuous regardless of throttle position. This seems to point to the breaker plate malfunctioning when vacuum is applied to the can or something I have not thought of.
                Any other ideas would surely be appreciated. I was hoping maybe Duke might have an idea as well. May just have to pull the dist and have it checked again.
                Thanks everyone,
                Brad

                Comment

                • Michael W.
                  Expired
                  • March 31, 1997
                  • 4290

                  #9
                  Re: Rare 69 427 Vacuum Advance Anomoly for the Experts

                  You haven't told us what the timing does when vacuum is applied.

                  Comment

                  • Timothy B.
                    Extremely Frequent Poster
                    • April 30, 1983
                    • 5178

                    #10
                    Re: Rare 69 427 Vacuum Advance Anomoly for the Experts

                    Sounds to me like the vacuum advance control is bad and when vacuum is applied either from ported or full manifold source the leak creates a lean condition causing engine miss.

                    Get a miti-vac and test the advance control to see if it holds vacuum.

                    Comment

                    • Joe L.
                      Beyond Control Poster
                      • January 31, 1988
                      • 43198

                      #11
                      Re: Rare 69 427 Vacuum Advance Anomoly for the Experts

                      Originally posted by Timothy Barbieri (6542)
                      Sounds to me like the vacuum advance control is bad and when vacuum is applied either from ported or full manifold source the leak creates a lean condition causing engine miss.

                      Get a miti-vac and test the advance control to see if it holds vacuum.

                      Timothy------


                      Yup, that's what I was getting at, too. I really don't see how it could be anything else.
                      In Appreciation of John Hinckley

                      Comment

                      • Stuart F.
                        Expired
                        • August 31, 1996
                        • 4676

                        #12
                        Re: Rare 69 427 Vacuum Advance Anomoly for the Experts

                        No doubt you guys are right about the VAC, as I have failed several in the past couple of years. But, not to the point of having a ruptured diaphragm, rather that they just wouldn't pull in at all, perhaps from a pin hole leak. If it is pulling in and holding, then the tipping plate has to be considered. My thought was that perhaps the re-builder didn't apply the spring clip. I have also seen several repo VAC's with bent/mis-aligned pull rods that caused a binding condition.

                        Stu Fox

                        Comment

                        • Brad H.
                          Expired
                          • January 26, 2009
                          • 250

                          #13
                          Re: Rare 69 427 Vacuum Advance Anomoly for the Experts

                          Thanks to everyone for the ideas. I'll check the can some more and probably pull the dist and do some more investigation there. Problem must be there somewhere. If you think of anything else don't hesitate to jump in.
                          Appreciate the help!
                          Brad

                          Comment

                          • Jim T.
                            Expired
                            • February 28, 1993
                            • 5351

                            #14
                            Re: Rare 69 427 Vacuum Advance Anomoly for the Experts

                            Brad the wire going to the points could be contacted or somewhat shorted out with the movement of the breaker plate by the vacuum advance. Replace the wire with a new one and see what happens. If the coil to points wire is the original, it is very old. I have seen on this board that NAPA carries a replacement for your distributor.

                            Comment

                            • Brad H.
                              Expired
                              • January 26, 2009
                              • 250

                              #15
                              Re: Rare 69 427 Vacuum Advance Anomoly for the Experts

                              Thanks Jim, I'll look at that. My distributor has all new parts so I assumed the wire was new but who knows.
                              Brad

                              Comment

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