CIS Strip Down

[echrisconnor]

I should be finishing up rebuilding my engine in the next month or so, and am trying to eliminate as much of the "extra" junk on the motor. One of the things I've been thinking about cutting down on is some of the arguably un-necessary CIS components.

My car is a '76 Carrera 3.0 with CIS and a hand throttle. It is driven exclusively in warm(er) weather. What I'm thinking about doing is pulling off some of the components and making it more like the CIS system of a 73-74 CIS car-- for the sake of simplicity.

This would mean removing the auxiliary air regulator and auxiliary air valve. So far, I've found that I can pull all that stuff on the right side of the engine, block the air outlet on the boot, and plug the inlet by the cold start injector. All other system elements such as the cold start vavle, WUR and decel valve would remain.

I could use the hand throttle for cold starts and otherwise I can't see a downside. I've seen this done on a few track cars without any problems.

Any reason not to do this? Any pointers?

[Paulporsche]

I don't see a problem with that setup since your hand control would do what the AAR and AAV do automatically. I would make sure I have an airbox popoff valve installed.

[echrisconnor]

Yup. Got a pop off (of course). That's what I thought. Since I've got the hand throttle, and don't mind the manual process, I thought it might be a good way to simplify and cut down on the addtional CIS stuff.

Would the starting procedure be different? Crank until it fires and use the hand throttle to maintain idle.

c

[RarlyL8]

I've stripped everything off my CIS motor as well.
Yep, that's the starting sequence.

[echrisconnor]

You say this is the CIS reduction 101. RarlyL8, what else have you removed? I can imagine the decel valve being next on the list, but wouldn't see pulling anything else beyond that.

[Andras]

Does that mean one can remove the WUR, the cold start valve, and all that stuff?

The implication seems to be that all we'll need is the actual airbox, the intake runners, and nothing else?

How can one add the hand throttle? I used to have one on my 1974 911, but my 1983 SC doesn/t have one.

Ideas?

[RarlyL8]

The only remaining CIS items on my car are the WUR and the Cold Start Injector.

These items are needed for a quick start up and during the warm up period, even if you live in a hot climate. My engine is a turbo so the WUR is manditory for other reasons as well.

My car doesn't have a hand throttle. I simply hit the key, and AFTER the engine starts I press the throttle and hold it at about 2000rpm until the engine is stable. This generally takes less than 30 seconds.

There are a few publications explaining the function of each CIS devise. Most are for emission control, most just allow extra air to move past the throttle plate. You need to determine the requirements for YOUR car in YOUR region of the world and strip accordingly.

[echrisconnor]

So the only additional thing you removed (beyond my list) was the decel valve-- right? I agree the WUR and cold start injector are critical.

[RarlyL8]

Correct.
The decel valve is a so-so deal. A turbo car will pop and carry on when you lift the throttle and the engine will quickly loose RPMs down to idle. This can be a bad thing depending on your driving habbits. A N/A car may buck a bit or have throttle issues as well. If in doubt I'd leave it. The device has more good points than bad and doesn't take up a lot of room.
The beauty of all this is that the system is componential. If you don't like the results seen after you remove the device you simply put it back on. How cool is that ?

[echrisconnor]

Yup, the fact that you can pick 'n pull with this system is great. I figured I'd pull the AAR and AAV while the engine is out, but that if I were motivated, I could put them back (not sure what might motiviate me to do so). The Decel valve is easy enough to just plug the vacuum line if I choose, or pull the whole thing in 5 minutes.

The goal: Minimalist CIS

Thanks for advice.

Chris

[echrisconnor]

OK, I have achieved minimalist CIS. I have also acquired strange running characteristics.

Here's what I've done:
Pulled the AAR and AAV, and plugged up the boots for them.
Rebuilt engine and replaced all vacuum hoses and inspected all boots and CIS connections. I truly can't find any vacuum leaks.
Set timing and dwell to specs.
Leaned the mixture 1/2 turn (seems to run better now and no, I have not checked it with a tester)

Here's what's happening:
When warm or cold, the car won't idle without a little hand throttle. Idles fine with a little throttle
I can't adjust the idle high enough with the idle screw.
I'm drawing very little vacuum and am not getting full advance on timing at 6000 revs.

Any ideas? I'm suspecting that when I pulled these components and replaced all hoses and injector seals etc. that I fixed a number of vacuum leaks. The car must have been tuned to run with additional bypass air. Not sure though why I'm not getting full advance which seems like it may be the result of a vacuum leak.

[RarlyL8]

What procedure did you use to set the timing? Did you set or check it at high RPMs?

[Paulporsche]

echris,

I am wondering if the mixture is still too rich. When you leaned it 1/2 turn, did the idle go up at all? If you lean it 1/4 more, what happens?

What color is your tail pipe?

Is your distrib OK?

Does the sensor plate in the mixture control unit move freely?

Have you checked your WUR and control pressures?

[echrisconnor]

I think the mixture may still be too rich. When the WUR leans out, the idle usually picks up a bit from where I've got it set with the hand throttle.

I set timing with a light when holding an idle of 950 rpm. I only get maybe 20 degrees of advance though at 6000. I believe the distributor is fine. When rebuilding, I cleaned and re-lubed it. The vacuum advance does not leak and does move the points.

Tail pipe has just a bit of black in it. I haven't checked my mixture yet - wanted to get close and then borrow a Gunson from a friend. The control unit plate moves very smoothly.

So I have two thoughts. 1. I'm still rich and need to lean out some more -- then my problems may go away. 2. Was the CIS system designed to have some bypass air from the units I removed? For example, the AAR never fully closes, it always has that little slit in it to allow some air even when fully warm. Do I need to create a leak, or adjust the minimum throttle stop on my butterfly to allow more air at idle.

[RarlyL8]

You've done many things at once, any of which could contribute. Barrow the gas tester and then check the control pressure. This car has points? I thought they had done away with them by '75.
I can't speak for the N/A '76 CIS components but I had the opposite problem with my system after the strip down. The car would idle too high, around 1300rpm. It is now adjusted all the way down and sits at 900rpm or so. This is with only a WUR and cold start injector. The "cure" was a combination of timing and A/F ratio at idle (actually %CO).

[cmonref]

Is there an adjustment screw that sets the "closed" position of the throttle plate. Left side of the throttle body, near the throttle plate shaft. If you cannot open the idle adjustment enough to obtain idle, then open the "closed" position until the idle adjustment becomes functional.

[RarlyL8]

Brian - I left this function until last. You wouldn't want to adjust the throttle plate until absolutley possitive that all other systems are correct. That would just add more problems.
What I found with my setup - which again is slightly different because it is a turbo - was that after the rebuild everything was just a little bit off. It litterally took me a month to tweek all the system components to work optimally on the fresh engine with freshly cleaned and rebuilt components. After all was said and done I didn't have to adjust the throttle plate at all.

[cmonref]

I see. I was addressing the "won't idle without the hand throttle" point, suggesting that you could set the idle up so you could address all the OTHER things, then finish -- as you say -- with the idle air adjustment. You note that you ended up with no adjustment -- I would have adjusted up, then back later to end up at the same point. Ya obviously done good!

[echrisconnor]

I'm in agreement that I should get everything else set properly before changing the throttle stop. I'm going to try leaning out some more and see where that gets me. With every incremental leaning, it seems to run better.

I still need to figure out the advance thing though. Hmm..

[Paulporsche]

Echris,

I am wondering if your engine is just being choked off by a too rich mixture.