What does this CIS microswitch actually do?
 

I consulted six books on air-cooled engine rebuilding, and similar topics, plus the Porsche Service Manual, and none of them described what this switch is supposed to do. Except for the Porsche manual, none of the books even mentioned it.

The Porsche book told how to adjust it, but what is it for?

It is adjacent to the throttle linkage and is near the back of the engine; part of the linkage actuates the switch on this box's top. Sorry the photo does not show the actual switch mechanism on the box top.

http://forums.pelicanparts.com/uploa...1490815529.jpg

The microswitch is there to activate the cold start injector. However, the switch is in circuit with the starter motor so both the starter motor has to be cranking and the microswitch closed to activate the cold start injector.

Side question, what years is this switch on?

Thanks

'74 and some '75's

This car is a '74, but the engine is a '75 S, so it fits right in.. Thanks for the replies.

Micro switch.......
 

Jerome,

Since you have a PSM (Porsche Service Manual), refer to vol. VI section 9 ('74 wiring diagram). Look at circuit #109 in the supplemental page (0.1-3/5).

F25 .........Throttle valve switch.
F26 .........Thermotime switch.
N17 .........Cold start valve.

Tony

I've got one of those too - '74S. If anyone can post up the PSM page with specs I'd be mighty appreciative.
Thx.

Charles:

1973.5 Wiring Diagram:
http://www.pelicanparts.com/911/911_..._CIS_Part2.jpg

Legend:
http://www.pelicanparts.com/911/911_...IS_legend2.jpg

I posted a link to the '74 schematic here the other day:
http://forums.pelicanparts.com/9529767-post8.html

Here's one to the '75.
https://www.dropbox.com/sh/oswepkzym8agnt6/AAAR8QHZ8BO3BbkSNqVwvL2Ma?dl=0

The micro switch was part of the early cis cars with the hand throttle lever by the hand brake. On the 1973.5 the cold start valve will activate any time the key is in the start position with the hand throttle raised. In 1974 start system was refined, and the thermal time switch was added. If the hand throttle is not raised, the cold start valve will not operate.
This is the part of the start system for the 1973.5 cis.
http://forums.pelicanparts.com/uploa...1490878887.jpg

Yep, my 1973.5T with the first CIS has the microswitch, BUT no THERMOTIME SWITCH as many suggest.

Bob
1973.5T

I have contacted Pelican a few times since 2014 regarding the fact that the 1973.5 cis does not use this. Unfortunately their response was
"Followup from the Pelican Staff: This part is used on the timing chain cover for 1973.5 CIS cars. For the MFI cars, it is used on the oil breather cover."
Yes it is on early '73 MFI and '74 on cis, but for some reason they refuse to accept the facts and continue to list it for 1973.5 cis.