> Hello all, I'm having a warm idle problem with my '77 Spitfire 1500. When
> cold it idles okay with the choke on, but when it's warm and I stop at a
> stoplight it nearly dies. It idles rough enough that it shakes the car, then
> I have to rev it up just to keep it running. However when I pull away from
> the light it runs just fine? I pulled into my garage tonite to adjust the
> fuel mixture and idle speed (I have a Weber DGV). I got it idleing the best I
> could but its still rough. I'm smell strong gas fumes? I adjusted the
> ignition timing a few days ago hoping this would fix the problem. It was at
> 18' BTDC and the decal on the inside of the hood says to set it at 10' BTDC,
> so I set it at 10' BTDC. Any ideas??
First, these are the classic symptoms of a vacuum leak. Let your car warm
up, then spray carb cleaner all around the carb base, the manifold, and any
fittings such as distributor advance pipes, gulp valves, etc. What I suspect
is that when the car is cold, the vacuum leak isn't there because the
metal hasn't expanded yet. When the car warms up, enough air comes in
through the leak that the car won't idle because the air-fuel ratio is all
wrong. When you step on it, enough air comes through the carb to make it
even out and the small leak doesn't matter.
The last time I had these symptoms were when I had plugged the manifold
inlet from the gulp valve after a problem with the valve. When the
plug failed, I immediately had the symptoms you described (plus a high-
pitched whistle from the kind of plug I'd used). A better plug (I have
to get a new gulp valve bracket one of these days) solved the problem
permanently.
As for your timing, I'm not sure about the Spitfire, but on the MGB (which
uses the same Lucas distributor), you're supposed to set the ignition to
whatever the timing value is *with the vacuum hose disconnected.* If you
set it with the vacuum hose connected, there will be a small amount of
vacuum advance operating when you set the timing, so your total timing
will be less than it should be.
Of course, if you did that but forgot to put the vacuum hose back on, there's
your vacuum leak. :-)
--Scott
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