Hot Idle Compensator and Lean Mixture

[Tham]

I'm currently using a 3K Aisan carburetor
on my 4K engine.

This carb doesn't hold idle very well, and
I think it's partly due to the return spring,
which is built into the throttle linkage,
unlike the 4K carb which uses an external
spring hooked to a bracket on the manifold.

I'm thinking of switching back to my previous
4K carb, which has a hot idle compensator,
which is basically a bimetallic strip.
This compensator introduces air into the
intake manifold at higher temperatures and
leans the mixture, and thus gives a smoother
idle too. The currrent 3K carb does not have
this compensator.

However, I've been told from the other posts
here that a lean mixture makes the engine
run even hotter, so I wonder if that might be
a problem.

[slide86]

yes, its true that a lean mixture does make the car run hotter.

have you adjusted the idle mixture screw? that could be causing your rough idle. If you wanted to add an external return spring, im sure that it can be achieved.

why is the 3k carby better than the 4k? just out of interest......

[Tham]

The idle mixture has already been fine tuned
several times. It's not the mixture screw.

The 3K carb is not better, just cheaper.
I changed to the 3K carb earlier as we
had initially thought that the 4K carb's
vacuum inlet (for the distributor's advance)
was faulty. It turned out to be the vacuum
diaphragm's plastic fine adjuster which
was melting due to the heat.