I answered most of my own questions. My Haynes CD carburettor manual has the
following to say about the device in question:
"The temperature compensator consists of a rectangular housing
closed by a plastic cover. It contains a bi-metallic blade,
one end of which is rivetted to the inside of the housing, with
an adjusting screw part-way along its length. The other end of
the blade engages a cylindrical plug with a conical end, which
slides in a cylindrical extension of the housing, forming a
regulating valve.
Variation in temperature of the bi-metallic blade causes it to
flex, moving the plug in its bore and regulating the annular
area around the cone, thus controlling the by-pass air bleed.
The adjusting screw enables a datum position to be set on
initial build. It must not be adjusted in service."
The blade is held in with a phillips screw, not rivetted (so the blade
assembly could be replaced without having to spring for a whole new unit),
and the adjuster is a tiny nylock nut, not a screw, but otherwise the
above is correct. Alas, it doesn't mention which way the blade moves.
When heated, does it withdraw the plug or insert it?
When the car's cold you want a richer mixture, so I'd expect it to be
closed, thus not allowing an air-bypass which would lean the mixture.
Neither of mine were closed when cold. Hmm. Time for an experiment.
A dunk in boiling water of the unit reveals it withdraws the cone when
heated, i.e. the blade flexes OUT, away from the carb body, increasing
the annular area around the cone, allowing an air by-pass and leaning
it out. Aha...
The little forbidden adjuster can be used to adjust the cold position of the
blade, so my only question now is:
Is it supposed to be COMPLETELY CLOSED when cold? Or was it
carefully calibrated for a certain anount of bypass, hence all
the warnings that you'd screw up if you change it?
If it's supposed to be closed, fine, that's easy. Tighten the adjuster until
the cone seats and you can't blow air by with the pursed lips test. Done.
Now if only I could get new covers I'd be happy. Anyone have a milling
machine? Or a perfect-condition cover I can do a lost-wax on? Jeez...
--ian
|