while I was derusting my airbox on a '80 343 1.4 with variomatic, I discovered, that the warm air intake was full open
at room temperature.
Reason is this little thermostat thing

which is now at room temperature. At this temp it should look like this

So this part is dead... and replacement not available.
So I ordered the airbox thermostat for 200/700/900 models. This thermostat looks quite similar and has the same
diameter, but is 0,3" too long.
To put it into work I had to dismantle the plastic holder and cut the spring to fit.
Now it looks like this:

I tested the solution and it works well.
Hope this helps others 343 users....
Regards
Ralf