cis idle question
 

I am a relative beginner when it comes to CIS. Car has been running great lately. But I just noticed the idle was a little low say around 800 or slightly below when engine is warm. It seems
the idle would float a little too as it fluctuates from 800 to 900.
I tried to screw in the idle screw about a half turn or so and it didn't seem to do anything. Could this be a vacuum leak? Anyone have any ideas? Thanks

A vacuum leak would normally cause a higher idle. Trying unscrewing (counterclockwise) the screw to allow more air in.

It's a balance thing, if you adjust the idle bypass you need to be ready to adjust the mixture as well. But yea, start by checking for leaks of course.

Injector O-rings
Injector bungs
Brake booster connection
Air box halfs
Cracks in the air boot
lose clamps on the oil breather hoses
Intake runner boots
Intake runner gaskets

It's also possible your mixture is a tiny bit rich. Try the CCW turn of the idle screw and let us know what happens.

So, let me get this straight. CCW increases idle and CW decreases? I turned the thing a 3/4 turn CW yesterday.

ael911,

The screw blocks the passage that allows air in for idle. By screwing it in (CW), you are blocking more of the air passage. By screwing it out (CCW) you are opening up the air passage.

Also check your points and timing to be sure nothing is changing there.

Thanks guys, I will go home and try CCW the idle screw

BTW I just realized my comment may be misleading. The idle screw doesn't affect mixture. That is done by the mixture screw on the fuel distibutor/mixture control unit. My suggestion was to try raising the idle first and see what happens. If that doesn't do it, then get back to us.

Ahh but it does, I can watch the CO go up and down with the idle bypass screw.

Okay, I will try the idle screw first to see what happens. The issue is really subtle as the rpms only fluctuates a little bit. But enough to where I notice it. I also notice the rpm will dip down to about 600 when I spin down and come to a stop without load. The rpms will then jump back to 800 or so and idle. The engine is warm and the alternator light does not come like close to a stall.

Your points may be going bad or need a re-adjustment. My points went wacko one to many times causing things like you described - pulled them and put in a Pertronix ignitor kit.

After putting in the kit plan on redo the timing, adjusting your idle speed and playing with your fuel/air mixture (mine is too rich right now) to get it right.

Scott R:

That's not what's supposed to happen. That air is supposed to be bypassing the throttle, not be added to the mix.

What change in CO do you get for how much of a turn of the screw? We're talking the big flat one here, right?

Yes the big flat one, to get a perfect .8 I have to adjust both, I plan on checking my mix later today when I am done working, I'll try and snap some PIC's and record the turns.

I run well at .8 but I like the power around 2.5 so I was going to bump it up.

The car already has a Petronix Ignitor...
Troy

Souk at MotoMotions went through the logic of CIS idle and mixture in great detail in the following thread. I can't say that I understand it all, but it comes from a great source:

http://forums.pelicanparts.com/showthread.php?s=&threadid=232089&highlight=CIS+id le+mixture

Hi guys, I turned the idle CCW a little bit this morning. Brought the idle to about 900. She seemed to run smooth. Deceleration valve seemed to be working better as the deceleration slowed down when the rpms came down to 1500 and slowly settled back to 900.

Troy, thanks for the post. I knew you'd be around.

Yeah, I'm skulking around, keeping tabs on the old girl and her new owner. ;).
Troy