<VV> engine vacuum/automatic trans

[iscdirector]

The motivation behind this post is two things. To tell if this problem I am seeing is as widespread as I think and to try and figure out a fix. The GM manual says that there should be at least 16 HG vacuum to the modulator at idle. I have seen several Vairs lately that have only 10 to 12 Hg at best and the vacuum gage (handheld) does not show a steady reading it is sort of vibrating. These cars have perfect carbs, timing set at 16 btd or earlier, and normal compression. Also they basically run ok except for harsh shift from neutral to drive and harsh downshift when coming to a stop indicating the modulator is not doing its job. I have experimented with a new modulator and it did not pull in and work until the vacuum reaches 15 HG. These cars also have a less than perfect idle in drive with brakes on. So I am asking if anyone has conected a vacuum gage to their engine and what type of readings you got. Also the only way I have been able to get the vacuum to steady out and
 come up high enough to operate the modulator correctly is to adjust the valves with a vacuum gage hooked up and set the rockers at zero lash. If the valves are tightened even a quarter turn the engine seems to smooth out some after a minute but the vacuum gage becomes unsteady again and stays that way no matter how long you wait. The vibration seen on the vacuum gage is turbulence in the intake manifold caused by compression coming back by the valves because they are unable to close completely unless the rockers are set at zero lash. So could anybody who has an auto car and a vacuum gage check their car and let us know what kind of readings you get with the engine warmed up and idling. All the cars I have looked at have aftermarket lifters and have been rebuilt at some point. Also I know for sure some do have new valve guides. If anyone else has tackled this problem and fixed it I hope to hear about it.  Thanks
 		
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