spridgets
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Re: vacumn advance

To: Paul Asgeirsson <pasgeirsson@worldnet.att.net>
Subject: Re: vacumn advance
Date: Wed, 05 May 2004 09:44:56 -0400 5.0; U)
Cc: Antony Gelberg <antony@antgel.co.uk>, spridgets@autox.team.net
References: <20040505111436.GA21186@brain.pulsesol.com> <002d01c432a2$024ce0e0$f675fea9@p0k7l8>
Yes, but....

When the vacuum signal is taken from the carburetor base, there is little or no
vacuum until the throttle is open.  Lines are disconnected and plugged at idle
because you want to eliminate any chance of advance since you won't know
precisely how open the throttle plate is at idle.  Then, at higher throttle
openings, there is more advance due to the increased vacuum signal.  The vacuum
present at the carb base is not the same as manifold vacuum.

Some setups take the signal from the manifold.  I just bought a used DCOE setup
at Britfest that has vacuum lines coming from the manifold, and the literature I
found so far suggests this is for vacuum advance.

Also, some technical specs suggest that vacuum advance is significant in some
applications.

I still have more to learn about this and Spridgets, though.  My 1098 still has
a goofy little stumble just off idle that's prevalent when you rev it in
neutral, but it's not noticeable under power.  Too rich a jet setting maybe
(I've had issues with this) but I still suspect timing is playing a role.

Jim

Paul Asgeirsson wrote:

> Typically the vacuum advance functions only at times of high vacuum.  That
> would be like idle, or cruising at part throttle.  It would not function
> when you give full or nearly full throttle at higher speeds.  It simply adds
> a few degrees advance to the dizzy.






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