CIS throttle switch questions

[Speed metal]

So the switch on the side of the TB with two terminals..The little guy that is integrated with the throttle linkage.. What does this sucker do? How to adjust it? The CIS primer mentions it, but doesn't seem to offer any insight.

[john walker's workshop]

Without the year, maybe it's the cold start valve micro-switch on 73/74??.

[Speed metal]

Sorry John, this one specifically.

[tirwin]

In the various Bosch systems, the idea is that once the throttle is opened to a certain point, the system needs to provide extra fuel to enrichen the AFR. JR posted a doc once that showed the states for different year models of the Bosch K-Jet from ‘80-‘83. I think the docs refer to it as angle of throttle opening measures in degrees. It’s basically a throttle switch though. The switch is either triggered or not. I have never seen anything describe how to adjust it. It’s a positional switch so unless it was damaged or bent I wouldn’t think there is a lot to adjust.

[Speed metal]

Originally Posted by tirwin

In the various Bosch systems, the idea is that once the throttle is opened to a certain point, the system needs to provide extra fuel to enrichen the AFR. JR posted a doc once that showed the states for different year models of the Bosch K-Jet from ‘80-‘83. I think the docs refer to it as angle of throttle opening measures in degrees. It’s basically a throttle switch though. The switch is either triggered or not. I have never seen anything describe how to adjust it. It’s a positional switch so unless it was damaged or bent I wouldn’t think there is a lot to adjust.

This switch opens(Currently) just off idle, at the slightest bit of pedal. Its an on/off switch essentially.. This enrichens the AFR?

[HarryD]

For the early CIS cars (73/74), it performed the function of the thermotime switch in later models. When the throttle was depressed, the switch closed. This completed a power circuit from the positive lead that energized the starter (when you cranked the car) to the 7th injector in the CIS air box to richen the mixture. There is a black handle between the seats that you pull up to start the car. It would move the throttle rod a bit to activate this switch and raise the idle.

[Speed metal]

Originally Posted by HarryD

For the early CIS cars (73/74), it performed the function of the thermotime switch in later models. When the throttle was depressed, the switch closed. This completed a power circuit from the positive lead that energized the starter (when you cranked the car) to the 7th injector in the CIS air box to richen the mixture. There is a black handle between the seats that you pull up to start the car. It would move the throttle rod a bit to activate this switch and raise the idle.

Ha! My engine is a real mutt.. Has a thermotime and also has this switch in question and no hand throttle.

[HarryD]

What is the year of your car? What engine does it have? is the thermotime switch hooked up?

[Speed metal]

Originally Posted by HarryD

What is the year of your car? What engine does it have? is the thermotime switch hooked up?

Motor is a 2.7 from 77.. Actually no thermotime!! Just checked on that.. My fuel hub has a 74 part number too

[tirwin]

Originally Posted by Speed metal

This switch opens(Currently) just off idle, at the slightest bit of pedal. Its an on/off switch essentially.. This enrichens the AFR?

You haven’t said what year model we’re discussing here so it’s hard to say. Edit: I see now the question has been asked and answered.

In the K-Jet w/ Lambda systems the brain cares about certain states. Engine is cold or not (various temp senders). Engine is at idle. Engine is a cruise. Input from O2 sensor is present. Engine is at WOT or not. It is a very primitive ECU by modern standards.

Going from memory, WOT is beyond X° angle of opening and where X is defined as a value I can’t remember off the top of my head. 15° is what jumps to mind but can’t say for sure. Anyway, once that switch is tripped it changes the duty cycle of the frequency valve to enrichen the mixture.

[HarryD]

Originally Posted by Speed metal

Motor is a 2.7 from 77.. Actually no thermotime!! Just checked on that.. My fuel hub has a 74 part number too

Where do those wires go?

Is your car hard to start? Do you need to work the throttle to get it to start and run when cold?

[Speed metal]

Originally Posted by HarryD

Where do those wires go?

Is your car hard to start? Do you need to work the throttle to get it to start and run when cold?

That's a pretty good question! They seem to disappear into the ether..
Its very easy to start, dead cold but I do need to press the throttle a bit to keep er running for about say 30 seconds. Almost like a hand throttle scenario.

[HarryD]

Where do the wires on the cold start valve go?

[Speed metal]

Originally Posted by HarryD

Where do the wires on the cold start valve go?

I wish I could see! I will take some more pics tomorrow in an effort to see where the heck they all go.. Any ideas Harry?

[T77911S]

the wiring looks aftermarket. don't know about the switch.

if you engine is a 77 it had no throttle switches.
now if someone put on a CIS form a different year that is a different issue.

if it does not have a frequency valve, then unless it is from a 73-74 (I don't know about switches on those either) then it should not have one.


that hose and crimp on the CSV could be dangerous.

I don't see a decal valve on there.

[tirwin]

Originally Posted by T77911S

that hose and crimp on the CSV could be dangerous.

Agreed. That looks sketchy. CIS operates at much higher fuel pressure than carbs. That thing comes loose and you'll be spraying fuel everywhere.

I was wrongly assuming you were talking about later CIS so my answers aren't going to help you.

Looks like you've got a cobbled together system. Maybe what you need to do next is step back and inventory what you've got on your hands and what problems you're trying to solve.

[john walker's workshop]

Yellow wires are between the starter and thermo-time switch on the left timing cover. The switch, when closed, (throttle open a bit to close the switch) completes the circuit. The CS valve wires both go to the thermo-time switch. When the TS heats up from the starter voltage, it relays starter voltage back to the CS valve, so 12v on both terminals on the CS valve keeps it from working on warm/hot starts when it isn't needed.

[john walker's workshop]

Cold start problem on 1974 911 2.7L CIS

[Speed metal]

Originally Posted by tirwin

Agreed. That looks sketchy. CIS operates at much higher fuel pressure than carbs. That thing comes loose and you'll be spraying fuel everywhere.

I was wrongly assuming you were talking about later CIS so my answers aren't going to help you.

Looks like you've got a cobbled together system. Maybe what you need to do next is step back and inventory what you've got on your hands and what problems you're trying to solve.

Easy now! It actually doesn't have any problems, I was literally just trying to find out what the heck that switch was for.. It runs nice! The switch just has quite a bit of adjustment, so I was pondering its function.

Originally Posted by john walker's workshop

Yellow wires are between the starter and thermo-time switch on the left timing cover. The switch, when closed, (throttle open a bit to close the switch) completes the circuit. The CS valve wires both go to the thermo-time switch. When the TS heats up from the starter voltage, it relays starter voltage back to the CS valve, so 12v on both terminals on the CS valve keeps it from working on warm/hot starts when it isn't needed.

Thanks John! This is what I wanted to know.

[Speed metal]

Originally Posted by HarryD

For the early CIS cars (73/74), it performed the function of the thermotime switch in later models. When the throttle was depressed, the switch closed. This completed a power circuit from the positive lead that energized the starter (when you cranked the car) to the 7th injector in the CIS air box to richen the mixture. There is a black handle between the seats that you pull up to start the car. It would move the throttle rod a bit to activate this switch and raise the idle.

This.
All of my CIS is 73-74... Checking part numbers confirms this. Also the lack of a thermotime switch.(which I mistakenly thought I had) What threw me off a bit was the year of my engine.