Reply to: RE>Runaway engine in Spit 1500
The problem you describe is probably related to the automatic choke used on
most all british cars in the late seventies. The choke is designed to enrich
the mixture during starting, and then gradually return the mixture to normal
as the car warms. The choke is actuated by a spring, and is turned off
automatically by the warming coolant, which circulates through the choke and
expands a wax capsule. The expanding wax pushes against the spring, turning
off the choke.
The way the choke is supposed to work is this. When you first get in the car,
you are supposed to tap the throttle pedel once, which takes pressure off the
throttle positioning cam in the choke and allows the cam to advance to its
highest setting. With your foot off the throttle, you then crank the car and
it starts (presumably). When the car starts, manifold vacuum is applied to a
kind of piston and cylinder gizmo in the choke that partly disengages the
choke when you tap the throttle to remove pressure from the cam once more.
So, when you first start the car, it should rev to something like 2500 rpm,
and when you tap the pedel, it should drop to about 1500 rpm. Then, as the
car warms, the wax capsule expands, and gradually shuts the choke off. Since
this happens while you are driving, you probably won't notice.
As you can tell from the foregoing, this choke is not simple: there's a lot
to go wrong, and I haven't the foggiest idea what's wrong with yours.
However, you can take the cover off the choke and watch it in operation
(mostly). Then perhaps you can see what the problem is. The cover is the
thing that has the water hoses running in and out of it. You don't have to
remove the hoses, just remove the three screws that hold it on and pull the
cover out of the way. Then play with the mechanism by flicking the throttle,
etc. Maybe one of the linkages is hanging up, vibrates and allows the
throttle positioning cam to advance after you start the car. May be the cover
is out of adjustment (it rotates to increase or decrease the amount of
choke). I don't know.
Good luck!
Scott St. Clair
'68 TR250
--------------------------------------
Date: 9/14/95 11:04 AM
To: Scott St. Clair
From: EMKolb@aol.com
Another problem with the new Spit 1500 (1978, no OD, new engine with less
than 100 miles on it). The car starts easily and idles at 800 RPM (per
original owners manual). After about 3 minutes of standing-still,
out-of-gear, never-touched-the-accelerator idle, the engine RPM leaps
spontanously to about 2500 and sits there. Knocking the little levers and
screws on the carb (single) doesn't do a thing. The one remedy I've found is
a quick depression of the throttle to take the RPM briefly to about 5000,
after which the idle drops back to 800. In the 15 minutes of so I've waited
after this maneuver it does not rev up on its own again. If this is some
problem related to the emissions control system, I'm not sure how much of
those devices are left after modifications by the PO(s). It just doesn't
seem like this is something the engine should do on its own...and if there's
something to adjust I would like to attend to it. ((I know, I know:
"there's always something to adjust on a LBC")). Thanks in advance for any
suggestions.
Ed Kolb
1978 Spitfire 1500
emkolb@aol.com
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From: EMKolb@aol.com
Date: Wed, 13 Sep 1995 22:49:41 -0400
To: triumphs@autox.team.net
Subject: Runaway engine in Spit 1500
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