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
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
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