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Ignition timing and vacuum advance?

To: mgs@autox.team.net
Subject: Ignition timing and vacuum advance?
From: Menno.Meijer@ict.nl
Date: Mon, 3 Jun 2002 13:09:25 +0200
Hello Experts,

The past weekend I've tried to verify and adjust my ignition
timing. (As far as I know this should be the step before
tuning the SU's)

First step: I've set the static timing to -10 deg. BTDC. (High
compression engine)

Second step: I've verified the dynamic timing, by using a
timing light. What I've found was that at 600 rpm the advance
was approx. -25 deg.! (Although, to the best of my knowledge
this should be -14deg)

Third step: I did the second step with the vacuum advance hose
attached. Because of the -25 deg. I've disconnected the vacuum
advance hose. The result was that the rpm seems to drop a little
(engine kept running) and the timing advance went to -15 deg.

My question: Although I've read a couple of books (chapters)
concerning "ignition timing" I'm not sure whether I should adjust
the dynamic timing with the vacuum advance connected or not. If
I should do this with the vacuum advance disconnected my timing
might be correct.

The reason for me trying to adjust the ignition timing is that
I expect that my SU's are not adjusted correctly. They seem to
be too rich. (Before adjusting the SU's I'd like to be sure that
my timing is correct)

Note: Instead of the "original" timing chain cover my MGB has
got a cover with the timing marks on the upper side. (5 indicators)
(I've verified that indicators are placed correctly. 0 deg. == TDC)

Best regards,

Menno Meijer '63 MGB

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