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Dear Drew:

I wouldn't do that. The timing spec was determined using subsonic detection equipment to optimize performance versus spark knock. Running advanced timing will cause advanced engine wear.

With such low vacuum I would start with gaskets given vacuum is still low after pluging the brake, distributor, and wiper lines. After that look for an internal leak in the choke stove, or carburetor mating surfaces. A worn throttle shaft will also cause such. The vacuum advance uses ported vacuum so won't cause such unless ports are uncovered at idle speed.

Drew, when I was in the process of negotiating the purchase of my car, the owner and I had several different in depth conversations because there was 425 miles seperating us and I didn't want to make the trip without being convinced that it was worth it. I was fortunate in that the gentleman I was dealing with was very honest and willing to tell me everything he knew about the car. In the process, he explained that the engine had a miss at idle but that as soon as acceleration occured it would smooth out. Once I decided to take a chance and make the trip, it turned out that the engine miss was the only issue that I found of any consequence with the car. The miss was indeed steady at idle and and cleared up at any speed above it. I speculated that it most likely had a valve that was burning or a broken spring but I also noted that the valve train was a bit noisy as well. once I got the car home I immediately pulled the valve covers and adjusted the valves which had satifactory results but I still had one valve on #3 that I could not silence. In the process of adjusting both valves I discovered that the exhaust valve had considerable side play between the valve stem and valve guide and pretty much determined that this was causing erratic valve seating. I trued up the lifter surface and valve stem with a file which helped quieten the noise a little but it didn't really help the miss however after I finished adjusting all of the valves, I moved to the air/fuel mixture and was able to adjust most of the miss out of the engine to where its mostly gone when the engine is warmed up. My compression numbers were not as healthy as yours so I didn't expect perfection, that will have to come later when I have time to perform a valve job and possibly install new rings. My point in all this is that it is possible that you have a weak valve that doesn't show up in a compression test but does when running...just something else to consider but with your engine's condition, I would say it's only a remote possibility.

Have you done a leak down test? I also had a slight miss at idle in one of my cars. It turned out to be a crack in the exhaust valve seat of the #6 cylinder. Compression was OK, but the leak down test indicated a problem with that cylinder. This was after doing all the tests and adjustments that you have already done.

Cheers,

Tom

As I said earlier and so did Tim, the big clue here is the low manifold vacuum. You've got to track that down and find the cause.

Quote:

Never heard of that kind of precision required on timing a 60 year old engine. But then, I'm not an expert. I left my subsonic detection equipment on my other workbench.

How much advanced timing will cause advanced engine wear? On what kind of gasoline? At what altitude? How advanced will the wear be, after how many miles?

Modern cars have knock sensors that retard timing when subsonic knock is detected.

Once on my modern car I had a sticking PCV valve which was causing subsonic knock. You could couldn't hear it but could feel the timing being retarded by the computer.

Since there is no DTC for the PCV the only way to figure it out was checking the basics. Oil consumption was up and there was ash on the plugs. So I started with the cheapest thing that could cause oil consumption.

One of the risks is that the timing is already advanced due to old advancer springs in the distributor. The only way to figure out what you are doing is to put the thing on a dyno and hook it up to scope. There using the factory advance curve the distributor can be tuned to the motor. A good analyzer will also show knock which shows up in the firing line on the scope. A good performance tuner can get up to 50 more horsepower just by matching the motor to the factory specs. That is why cheap modern cars blow off all those "muscle cars". They use a computer control to adjust performance to actual conditions.

The rest is just shade nonsense.

However those machines have largely been abandoned due to fuel injection.

To comment on the unanswered part of 55PackardGuy's question, heavy detonation (spark knock) if kept uncorrected for prolonged periods of time can lead to piston head erosion and in the extreme, piston failure.

What is the brand and NUMBER ON THE spark plugs?????

I'm assuming at this point the vacuum leak (indicated in post 1) has been corrected by tightening the manifold bolts.

Also that he plug wires have been seperated so as not to cause cross fire.

If the miss can not be isolated by removing one plug wire ata time then most likely it is improper plug heat range, cross fire of plug wires or maybe worn distributor bushings. THise are the easiest to diagnose/remedy. Carb/fule comes next.

What is the number on the spark plugs????

The plugs are Autolite 308. I'm not getting cross-firing, and my distributor bushings are good (the distributor was just tested).

The vacuum leak on cylinder #1 is gone, but tightening the manifold bolts has done nothing to address the low vacuum reading. I've got an nos set of manifold gaskets to try, if I get the courage and strength to take the manifolds off again, but I would like to KNOW that my problem is a leaky gasket before I go through that process, and so far, the tests don't indicate that I have any more leaks there. I've run enough propane around the manifold to power a Carolina Pig Pickin' without any change (and if I was leaking enough to misfire, I'd get a smoothing out).

Certainly no problem with Autolite 308 plugs, almost everyone I know with a flathead Packard engine with 14mm plugs runs them with satisfaction. Good luck tracking down the reason for the low vacuum, I guess you've already blocked all the lines at the manifold to eliminate things like wipers, booster pump, etc., and have checked timing and idle mixture? - misadjustment of them could easily account for your difference. How about severely worn throttle shaft bores and shaft in the carburetor base?