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Vacuum advance

To: (mgs)
Subject: Vacuum advance
From: (Todd Mullins)
Date: Tue, 9 Jan 1996 11:00:34 -0600 (CST)
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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