<VV> low vacuum

[Brent Covey]

Vacuum readings will be lowish if you live at high altitude-

Usually the jumpy vacuum guage needle at idle indicates the idle mixtures
are off, usually too-weak. Try setting the mixtures THREE turns out,
balancing the carbs for correct idle speed, and then re-setting mixtures by
'lean roll'- this means turning the screw in slowly on one side until the
exhaust note starts to sound a little more 'hollow' and the engine speed
starts to *just* slow down a trifle, then back out 1/4 turn richer from that
point- then do the same on the opposing side carb. You can chase it back and
forth a little to get it perfect, and on a Powerglide this can be done for
extra smoothness by adjusting it idling in Drive range with the wheels
chocked and parking brake set.

Many people start setting idle mixtures from 1 and a half turns out which is
too lean on some cars these days, so start a little further out and work
your way in. If you have very lean (like factory 49 jets) calibrations
they'll lose vacuum also.

Good luck,
Brent Covey
Vancouver BC
----- Original Message -----
From: "Dan Kidder" <iscdirector at yahoo.com>
To: <virtualvairs at corvair.org>
Sent: Saturday, September 02, 2006 6:32 PM
Subject: <VV> low vacuum


> I am looking for input on the subject of low vacuum readings. All the
corvairs I own as well as all the ones I have checked belonging to other
people have readings about 12 to 14 Hg. in neutral gets worse in drive 8 to
10 Hg. Also the readings are very erratic the needle on my handheld gage
vibrates and jumps. All the engines I have checked have aftermarket lifters,
some with many miles, some fresh. This indicates valves not closing. I have
tried replacing valve springs and it no effect. The only thing that seems to
raise the vacuum any is to run rockers at zero lash then it gets much
better. This problem is bad with powerglide as the modulator quits working
when vacuum drops below 15 Hg. Any one else addressed this problem it seems
to a common one as others in our club say they are having the same trouble.
>
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