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Vacuum advance

To: (mgs)
Subject: Vacuum advance
From: (Todd Mullins)
Date: Thu, 11 Jan 1996 10:05:47 -0600 (CST)
I sent the following message out a few days ago, but haven't seen it
show up yet.  Apologies if any of you get it twice.

> I've learned a _lot_ of things from you people, and I know lots of neat
> little things about the way my MGB works.  But I'm still unsure of the
> exact function of the vacuum advance.  Folks say that it helps
> driveability and emissions at idle, but can somebody explain the
> physics?  Is it simply a more complete burn while at idle?
> Anyway, I pulled the dizzy yesterday and confirmed what I suspected:  My
> vacuum advance unit was frozen.  Lots of WD40 and tugging later, it
> moves, but I had expected it to move a lot easier.  Actually, I had
> expected to be able to suck on the vacuum hose and watch the little guy
> go back and forth.  As it is, it takes a very firm push to move it.
> So what's normal?  Is my unit shot?  Do new units move easily?  How much
> vacuum does the 18V make at idle?  Will a functioning vacuum advance
> cure my backfiring on overrun (my thought is no; it's probably a frozen
> gulp valve...)?
> Once I get it working, how many degrees of vacuum advance should I
> expect at idle?
> -- 
> Todd "so many questions..." Mullins
>  On the lovely Mississippi (USA) Coast
> '74 MGB Tourer        in pieces this week
> "A life lived in fear is a life half lived."

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