[henrydbrown]

My 81 911SC idle was "hunting" about 50rpms or so and I knew my Pop-off valve was leaking a little so I replaced the popoff valve and attempted to turn my mixture adjustment to the left (lean) 1 click for spring time. Other than the barely perceptible idle wander/ hunt, it was running great.

Now the car will rev to 2000 rpm when started, then immediately idle down to 450 and will struggle to remain running. If I can nurse it with the throttle long enough to warm up for a minute (backfiring every few seconds), it will then rev up to 2000 rpm and remain there until I shut her down. When I restart the car, whether cold or hot, the cycle starts over again.

Looking in the air box, there is a silver damper arm (?) that hangs below the fuel distributer. Sometimes it is down and moves freely, sometimes it is up and does not move at all.

I'm stumped.

[VaSteve]

Put it back where it was, check your voltage at the battery and report back.

http://dorkiphus.net/porsche/showthr...hlight=battery

[Noah]

Originally Posted by henrydbrown

Looking in the air box, there is a silver damper arm (?) that hangs below the fuel distributer. Sometimes it is down and moves freely, sometimes it is up and does not move at all.

I'm stumped.

that arm is what connects the venturi sensor plate to the plunger in the fuel distributor. it's how fuel is metered in a CIS system. if you don't know what it is, allow me to suggest -- please do not take offense, as CIS is a complicated and finicky thing to deal with, even for someone with some DIY experience -- that you bring your car to a professional. also, the mixture screw on CIS does not "click," and it should not be adjusted seasonally, or without verifying your CO with the proper equipment.

there could be a number of sources for your problem and it'd be best to have a CIS expert go through the system, check fuel pressures, the functionality of all the components, etc.

[henrydbrown]

Steve,

I'm assuming you are saying put the mixture back where it was. I don't think I can do that b/c I wasn't getting the familiar "click" I got last fall when I turned it to the right for winter. That silver "dampener arm" I'm referring to is the housing for the mixture screw and I think that when I was trying to turn the mixture I wasn't always hitting the screw this time.

If you are saying put back the pop-off valve, the new one is epoxy'd in.

BTW, it has a new accumulator, WUR and AAR.

[VaSteve]

Yes, put mix back where it was. At least check the voltage to rule that out.

[Dr K]

Originally Posted by Noah

please do not take offense

Who are you and what have you done with Noah!?

Peter

[86911TLCAB]

When the engine is not started, you should be able to push up against that arm and get some light resistance, let it go and it should drop freely. When running it moves up and down based on the sensed need to adjust the fuel air mixture.

Sounds to me that your mixture is definitely off. amazing how fixing a single leak can cause a change in the dynamics of the CIS. I would make further adjustments to the fuel air mix with a CO2 guage telling you what the level of CO2 is. Otherwise you are just guessing.

I dont recall any clicking when i was playing with my adjustment. if you were getting some clicking might have another problem. Also, out of curiosity, how much were you turning the adjustment. Did you ever turn it all the way around a full turn or was it only slight adjustments? Did you make any adjutment to the idle screw after you replaced the pop off valve. After you get the car warmed up, you might try to bring the idle down by turning the screw. But again, the CO2 level is the key to getting the right fuel air mix (presuming you dont have any other air leaks).

[VaSteve]

I think there is a spring under the mixture screw. I could see it as "clicking" if you felt the resistance of the spring against the screw head*. It's not indexed so that clicking would be at random.


*I just worked on the carbs on my bike so I might be getting it confused.

[henrydbrown]

Clicking!? - I adjusted the mixture last fall according to all the threads that suggested it on Pelican and I thought this forum as well. Glad to hear that there isn't supposed to be a click and that my memory is incorrect. I never turned it more than 1/16 turn at a time and noted in my book that I turned it 3/16th right last fall.

I just turned the mixture adjustment approx 1/4 turn back to the right, then played with the idle after it was warmed up. It appears to be running normally. Now I'm going to let it cool down and see how she runs from a cold start.

What is the most economical way to get to a CO2 sensor?

Steve: With the ignition off the battery puts out 12.75 volts. With the engine running the battery puts out 13.65 volts.

Noah - no offense taken but the way I'm learning is by doing. Now I know "that arm is what connects the venturi sensor plate to the plunger in the fuel distributor".

I know this CIS stuff is complicated, but with this board (& Pelican's) help I isolated & repaired my accumulator once and my WUR another time. Didn't know what they were either, but now I do. So I'll stick with it till I'm out of options or patience.

So, what's the best way to get my hands on a CO2 sensor?

Thanks for all of the help! Hank

[Noah]

http://www.innovatemotorsports.com/products/lm1.php