Sometimes it helps to see if the idle smooths out by stifling the air intake
a bit (a hand covering it partially should do the trick).  This usually
indicates a vacuum leak and could save a wild goose chase if it's something
else...

bill

----- Original Message -----
From: "Scott G. Terry" <sgterry@ENGINEERING.UCSB.EDU>
To: <vanagon@GERRY.VANAGON.COM>
Sent: Friday, August 17, 2001 10:18 PM
Subject: do we have a vacuum leak?

> Hi Michael,
>
> Thanks for responding to my post.  I'll be interested to read your
results.
> Please carbon-copy me when you post them to the list.  I subscribe in
> digest-mode and don't always have time to keep up with the traffic.
>
> Pearl is fluctuating rapidly between 7-9" vacuum at idle so I think by
> anybody's standard I do have a leak.  Lucky me!
> I think I can hear a leak but I can't get the engine to race when I hose
> suspect areas with carb cleaner (not the safest approach, use cat.
> converter safe brand, etc. etc.).  Maybe a worn valve train... maybe I'm
> just hearing induction noise...
> this is where experience (which I lack) would really help.
>
> So is 10-12 " indicative of a healthy vacuum or a leaky vacuum?  I believe
> the question remains unanswered.  My conclusion from my test was manifold
> vacuum should be 15".  Yet no one has stepped up to the plate and said
> they're getting 15" in their wasserboxer.  Matthew Pollard is getting
> awesome gas mileage in his 1.9L(?) and I think I remember that he brought
> his fuel pressure into spec with a new FPR, so this would imply his engine
> has good manifold vacuum.  So, Matthew, how about borrowing a vacuum gauge
> from UI and measuring your manifold vacuum at idle (and maybe 2000 rpm
> while you're at it)?  We would make you second author if we publish the
> findings in the Journal of Vanagon Vacuum (J. Van. Vac.).  First author if
> you also do some NMR on the head gasket adhesive and solve the riddle of
> the water leak.
>
> Scott Terry
> '85 Westy "Pearl"
> Santa Barbara, CA
>
> >While attempting to evacuate my AC system, I noticed the MV as 10" to 12"
> >Hg just as you state.  Do you think I have a leak somewhere -- I hadn't
> >thought that it might should be 15".
> >
> >Thanks,
> >Michael Townsend
> >90 Carat
> >Durham NC
> >
> >PS.  Finally got my R-134a charged this morning -- looking forward to a
> >cool drive home!
>