<VV> Too much vacume at idle

[Barry Gershenfeld]

>It is apparent I am getting way too much vacume at idle.  Its at 14
>degrees, and steady with the va and carbhose plugged.  As soon as I plug
>in the lines correctly it
>shoots up to way off the guage.

There was a post last week about weak springs in the vacuum advance 
unit.  The following are observations rather than hard facts, but it sounds 
like my experience involved one of those "weak" units.

When you open the throttle the engine tends to speed up, but without any 
spark advance it doesn't really have that much effect.  The spark timing 
has a lot to do with engine speed.  Now, they tell you to check the timing 
with the vacuum advance disconnected, so I always do that.  But being 
curious I always check it both ways, to find out what difference it 
makes.  It turns out that with a good engine and everything set correctly, 
it wont change the timing.  This is because the vacuum port is closed at 
idle.   Now, if we go back to reality, and the kinds of engines that are in 
my cars, you'll often find that the idle is adjusted up from spec. a bit, 
so that the engine runs reliably.   Doing that opens the carbs a bit, 
supplying vacuum to the v.a.  That in turn will bring the advance in a bit, 
and the engine will speed up.  The increase in speed results in an increase 
in vacuum, which will pull on the v.a. some more, and as you can see, the 
engine wants to go to a high idle with full vacuum advance.  Whether it 
does or not is partly related to the aforementioned spring.  The result of 
all this is a situation where you just can't find a "happy" idle 
setting.  The engine either wants to quit or idle 800-1000 rpm.

This is only peripherally related to your problem, but hopefully sheds some 
light on what's going on under the decklid.  It can help to point out good 
or bad things you can do, and the consequences.  And if that "weak spring" 
seems to be your particular problem, look back to 7/17/04 and Larry 
Forman's excellent post on the v.a. and the fix.

Barry