CIS starting procedure

[jrairplane]

I have more than 6 shop manuals for my 74 911S with CIS but I can't find where they explain the proper starting procedure. Since the start enrichment valve is not energized unless the throttle is depressed (this closes the microswitch) it would seem that you need to depress the throttle when starting a cold engine. This seems wrong for a fuel injection system.

Could my microswitch be screwed up?


Any advice will be appreciated

[ossiblue]

Your 74 should have a hand throttle on the left side of the emergency brake (the throttle has a black knob, the heater is red.) Pull the throttle all the way up and start the car. The throttle will activate the micro-switch and the car will fast idle. When car is warm, or after a few minutes, push the hand throttle down and the car should idle at the proper range.

[fred cook]

On my '80SC w/CIS I simply turn the key and it starts! No throttle needed. Sounds like you have an adjustment problem. If you have a manual throttle control lever, pulling it to the rich setting should activate the micro switch (I think). Good luck!

[HarryD]

Your car should be like mine with a BLACK hand throttle near the handbrake and RED heater lever.

When you start your CIS, Lift the hand throttle which does two things, opens the butterfly a bit and hits a microswitch which energizes the cold start injector when you hit the starter motor. DO NOT TOUCH the accelerator pedal. Once the car starts, adjust the hand throttle to a 1500 (more or less idle). As the car warms up, you can close the hand throttle.

Here is some disscussion on the topic: 74 cis 911 cold start woes

[HarryD]

Originally Posted by fred cook

On my '80SC w/CIS I simply turn the key and it starts! No throttle needed. Sounds like you have an adjustment problem. If you have a manual throttle control lever, pulling it to the rich setting should activate the micro switch (I think). Good luck!

Fred, you guys got is so easy....

[Porsche-O-Phile]

Same here. I don't think any of those levers actually do anything on my car (I know for a fact the cable for the heat exchangers is popped off under the car so I have to reconnect it). The other one? Shoot, I thought it was an ejector seat or somethin'.

Never had a problem starting here. I'll check - bet that cable's popped off too.

[vash]

i thought i read, no throttle. causes backfires?

[HarryD]

Originally Posted by vash

i thought i read, no throttle. causes backfires?

That's right. Leave the accelerator (throttle pedal) alone when you are starting, just the hand throttle. Unlike a Carburator, no pumping etc is needed.

[Jay Laifman]

That's what I've always known about and done. But, recently I took a look at that throttle lever because it was out of adjustment. What I think I found is that it is not a separate cable or anything. It's just the accelerator itself. There is a plastic barrel around the cable. When you lift the throttle lever, it pushes on the barrel and moves the accelerator cable's resting place, which lifts idle and hits the microswitch As far as I can tell, lightly pushing the gas pedal does the same. So, why all the fuss over starting with the pedal? I can only think of two things: (1) it stops the pedal from being pressed to far, and (2) it is more constant than perhaps someones foot that might fluctuate. I don't know how those contribute to backfires and blown boxes.

[HarryD]

Originally Posted by Jay Laifman

That's what I've always known about and done. But, recently I took a look at that throttle lever because it was out of adjustment. What I think I found is that it is not a separate cable or anything. It's just the accelerator itself. There is a plastic barrel around the cable. When you lift the throttle lever, it pushes on the barrel and moves the accelerator cable's resting place, which lifts idle and hits the microswitch As far as I can tell, lightly pushing the gas pedal does the same. So, why all the fuss over starting with the pedal? I can only think of two things: (1) it stops the pedal from being pressed to far, and (2) it is more constant than perhaps someones foot that might fluctuate. I don't know how those contribute to backfires and blown boxes.

Jay, you are correct that you can use your foot but the amount you open the throttle is so slight it is hard to do consistently. The cold start injector is to simulate the extra jolt of fuel you get when you close the choke plate and pump the pedal on a carburator.

IMHO, if you open the throttle too much, you get a a really rich mixture (cold start injector plus flow from fuel distributor) that causes, first a failure to start due to flooding, and then the backfire from excessive fuel in the intake.