What's this part?
 

Here I am, happily installing the chain tensioner update when I notice this part... part #31 on this diagram http://www.pelicanparts.com/911/911_Parts/1974-75/1-4.JPG . What is it? :confused:

Sure would help if you gave us a clue which engine you have???

On CIS cars, that is the Thermo-Time Switch for the Cold-Start circuit. Other cars just leave the plug in the chain cover in place.

Temperature sensor.
(What do I win?)

:) Thanks! You guys are really FAST!

Early_S_Man: Uh, sorry about that http://www.pelicanparts.com/support/smileys/pray.gif. It's a 75 CIS that's being converted to carbs (after overhaul) and finding a home in my 914.

Doug Zielke: A used '75 CIS setup? :D

Since I won't be using CIS, I guess I'll leave it off. BTW, the chain tensioners are insanely easy to install with the egine out of the car.

Trivia..on my CIS the part is a thermo- time sw.......Ron

The thermo-time switch triggers the cold start injection valve (injects extra fuel into the intake rail ONLY while cranking and ONLY when cold). You won't need it on a carb conversion.