Vacuum advance is a load sensitive device designed to provide the maximum
amount of advance under all load conditions. Under low load (high vacuum)
the timing is advanced for increased performance. Under high load (low
vacuum) it is not safe to advance the timing too far or you'll get pinking,
so the timing is retarded a little bit just after you stomp on the throttle
pedal.
(and I LIKE stomping on the throttle pedal). ;{)
Vacuum retard is a device designed to provide a smoother idle. If you
advance your Triumph's timing a little bit at idle but touch nothing else
you'll see the idle RPM go up. If you retard the timing you'll see it go
down. The vacuum retard device takes advantage of this phenomena and
dynamically adjusts the timing to keep the idle RPMs as constant as possible.
Here's the fun part: some Triumph distributors have BOTH vacuum advance and
vacuum retard on a 'two horned' distributor. At idle the vacuum retard unit
keeps the engine running smoothly. As soon as car starts moving the vacuum
advance takes over.
-Erik
At 09:50 PM 9/25/2001 +0000, sujit roy wrote:
>What is the difference between a vacuum retard and a vacuum advance unit?
>My US Stag was fitted with one type, vaccum advance I think, but is no
>longer available. I bought the other type and want to know what changes to
>the timing do I need to make the car run right.
>
>Thanks Sujit
--
Erik Quackenbush, V.P. Operations, Midwest Filter Corporation
1-847-680-0566 fax: 1-847-680-0832 http://www.midwestfilter.com
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