[TR] 1980 Spit: vacuum retard

[Tim Gaines]

My Spit distributor has the vacuum retard unit, and you are probably 
right about too much bother to try fixing it.  The emissions stuff is 
long gone, and it idles nicely already at a steady 850 rpm.  However, 
when I got my 1974 TR6, also with the retard unit, I couldn't get a 
nice, low, steady idle until I reconnected the unit.  It really makes 
a difference on that car.  I was surprised because many on the list 
advised leaving it disconnected.

The rest of the story is that I have 1980 Spit parts car, also with a 
busted vacuum unit.  That car was a lucky find, built two weeks after 
mine, cheap, and sitting just 50 miles away.  Anyway, I may try to 
get into one of the units just to see what's what.

Tim
1980 Spitfire
1974 TR6

At 12:08 AM -0400 6/3/09, Jim Muller wrote:
>On 2 Jun 2009 at 9:38, Tim Gaines wrote:
>
>>  Has anyone ever been able to repair a vacuum advance or
>>  retard unit.
>
>Nope, but I'm not sure it's worth the trouble.  Well, if it is rigged
>to produce a retard at idle then it is part of the emissions system,
>so that's a reason, more or less.  But without the rest of the system
>in place the effect is minimal.  When my '80 Spitfire's air pump
>seized a long time ago I disconnected everything, then ran it through
>state inspection with the vacuum retard hooked up and not hooked up. 
>It was marginally cleaner with the retard, so I left it in place. 
>But it was not so much dirtier that I would have worried about it if
>the diaphram was broken.
>
>If the diaphram provides advance via manifold vacuum, it is for extra
>power at part throttle, sort of.  More specifically, it advances the
>ignition a bit when the intake air charge is less dense due to the
>throttle being not open fully.  This give you more power at part
>throttle, but it isn't really necessary because if you want more
>power you can always just open the throttle further.  When the
>throttle is fully open you have no vacuum advance at all, i.e. the
>same as if it was disconected.  So what's the point?  It gives you
>marginally better fuel mileage at part throttle.  Does that matter in
>a Spitfire?  Well, of course, but not so much as for a heavier car
>with a bigger engine.
>
>
>--
>Jim Muller
>jimmuller at rcn.com
>'80 Spitfire, '70 GT6+
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