CIS question?

[ClickClickBoom]

Hey,
I am chasing down all those little detail gremlins that CIS tosses our way. My latest is after removing the vacuum hoses for the air injection and capping the inlets, I still have one small issue. When I run it hard and let off the throttle quickly the RPMs drop almost to stall and then pick up to about 850ish steady RPMs. I have removed the air pump and all the associated chunks. I am chasing small, really small vacuum leaks, and I wonder if that could be the cause?
Inquiring mind
eric

[snbush67]

Yes, that could be it.

[T77911S]

not likely. when the the rpm's drop like that, it is a sign of being too rich. not sure, but i think the smog stuff leans it out, so removing it may be the cause of being richer.

[Hladun]

Congratulations, you've plugged your vacuum leaks. Now when you close the throttle, the manifold vacuum goes high (no airflow) and the engine goes rich and stalls. Eventually the WUR catches up (leans out) and it keeps running. The decleration valve is meant to cure this problem.

[Wyvern]

Also just learning ...

And the Decel valve is adjustable ...

How is it adjusted ?
(what direction - in / out - does what ?)

[Hladun]

Take off the small vacuum hose on top and losen the locknut. If you turn the nipple clockwise (in) the valve will open at higher vacuum (and eventually not at all). Turning it counterclockwise(out) will have it cut in more. When set right the engine should "hang" for a few seconds and then go to idle.

[ClickClickBoom]

Hey,
I went out and loosened the top nipple, sucker was tightened down all the way. I unscrewed the sucker and got some hang at about 1500RPMs. I still get a little drop below 950RPMs. I guess I still have some more leaks!
Hola
eric
P.S. The rest of the CIS works flawlessly, runs like a champ and gets 24MPG to boot!

[T77911S]

go have thr CO checked. my decel valve is removed and i am running pretty rich and my car does not dip when i let off the throttle, it is right on the edge, bit no dip. my CO is 3-3.5%.
BTW, that is a good way to set the mixture if you do not have an analyzer. i set it just on the edge of wanting to dip or hunt at idle, which ever happens first. then i check it with the LM2 to see if what i am doing works.

[Paulporsche]

As T77911s said, you may not have any leaks. Your mixture may simply be still set too high. Leaks per se usually don't cause the drop in idle that you mentioned. Sometimes setting the CO too high to make up for problems like leaks can cause it however. So can a poorly functioning WUR.

A shop ought to be able to set it for you inexpensively and give you a known figure you can reference.

Or you can try leaning slightly more (like 1/16 turn) until the dip goes away and see what happens.

You can also try searching Souk and his Push Pull method of setting CO. It involves pushing and pulling on the sensor plate while the engine is idling.