Packard Forum Index » Pre-War (1899-1942)

I am going over a lot of 'small stuff' on my car this winter and one of the items on the to-do list was take the distributor out and lubricate the advance mechanism and confirm my Vacuum pot is functioning properly. I did this and found it made quite a difference with the way the counter-weights 'snapped back' after the vacuum was released as opposed to the slow movement prior to being serviced. Then I wanted to check the ACTUAL engine vacuum (I checked the dist. with a hand pump) so I hooked up a gauge to the intake manifold. With the engine running at a nice idle (+/-700RPM) the gauge registered right on the border of red and green, about 15/16 inches of vacuum. The engine is a fresh rebuild and has lots of power, any ideas why I wouldn't be up around 20 inches or so on the gauge?? The gauge also flutters ever so slightly and the performance card suggested bad plugs, so I replaced them. The old ones looked fine and all exactly the same. I haven't run the engine since I redid the plugs as we have had a cold snap suddenly and it's -15, so I don't want to even try. The gauge shows all the other functions as normal, i.e., when revved, it drops momentarily and then goes into the green for a sec and then back to the idle reading. Anyone have any thoughts re the 245 and what it SHOULD develop for 'normal' vacuum?? And am I checking it in the correct place by using the threaded hole in the intake or should I be reading off the carb?? I DID check that all nuts and bolts were snug on the manifolds, and it sure idles nice and revs responsively... Chris.

Your engine in healthy condition and in good tune should give 18-20 inches of vacuum at idle. Very small changes in ignition timing and/or idle mixture could easily account for the slightly lower value you're seeing. Assuming you've checked for a small vacuum leak.

Slight fluctuations (a half inch of vacuum or less) doesn't represent anything to necessarily be concerned about as long as the engine is performing well, good even compression, etc.

Altitude above sea level will also affect the vacuum reading.
You can expect readings to be about 2 inches of vacuum lower in Princeton, BC at 2100 ft so 16 to 18 would be good.

Thanks Dave & Brian. Like I said, have installed new plugs and as soon as it warms up enough, I will start it up and try adjusting the timing and carb mixture a bit and see what it does. What you say about altitude makes sense Brian, as I remember when we were kids and would take a trip down to the coast, I recall having a screwdriver in the glove box and having to adjust the carb on whatever old bucket I was driving. I suppose modern cars have sensors that auto-correct that nowadays.
Chris.