Ballpark adjustment of CIS idle mix

Macel · 06-14-2006, 01:21 PM

Right now Im just trying to get a ballpark idea of where that idle mix screw needs to be set in order to get the car started so I can further adjust it properly. I know that screw is extremely difficult to even see, no less get a picture of.. Is there a diagram somewhere that can show me whereabouts it should be?

Elombard · 06-14-2006, 02:01 PM

Are you talking about the mixture or the air bypass screw? The idle speed screw (air bypass) is on the drivers side on the side of the TB - big giant screw cant miss it. The mixture screw is down inside the fuel distributor. You need a 3mm allen that is a little longer than normal. If you take the intake snorkel off you can see a little hole next to the turtle looking rubber thing.

This is a very involved deal, you should probably check a bunch of stuff before adjusting the mixture, if you do a search you can stay up all not getting educated, there is lots of pictures in the posts with the exploded factory diagrams. Once you get an understanding of the system its pretty straight forward. Dont rush it!

MotoSook · 02:25 PM

Here is the mixture screw:

In a previous thread you mentioned that it might have been turned clockwise to the max. and is stopped.

I would unscrew it the mixture screw (turn it CCW 2-3 turns from full lock-CW), then see what happens. Keep in mind that your cold start/idle circuit is active if the engine is cold.

So! Since you do not know your baseline (prior to you turning the mixture screw), you will have to back off the mixture screw until you have a decent idle. Then let the car warm up or drive it around the block. That will get the engine warm enough to get it out of the cold idle operating conditions. You do not want to adjust the mixture unless the engine is at operating temperature (control pressure at normal, and AAR closed)

Paulporsche · 06-14-2006, 02:30 PM

Do a search on The Push Pull Method of checking your mixture setting without a meter.

Also, as a rule of thumb, provided all components are in good working order:

If the idle oscilates, your mixture is probably too rich.

If you get backfiring through the intake, your mixture is probably too lean.

If, when approaching a stop, the engine momentarilly drops its revs and wants to stall, it's too rich.

If the engine feels choked off and doesn't rev freely to redline: too rich.

If you get a little burbling sound from the exhaust on overrun: probably just slightly too rich.

Macel · 06-14-2006, 04:15 PM

Thanks for the help guys.

It was actually turned all the way counter-clockwise. I've found the range of play for the screw to be quite wide (like on the order of 30+ complete revolutions, maybe twice that much, not sure... Wasnt really keeping count. However I noticed that the screw itself is discolored after a certain spot - which suggests to me that the line is where the screw was sticking out originally..

Took a picture for the heck of it.. didn't come out very well, but you get the basic idea of what I mean..

Anyway, I tried putting it back at that setting and the car still won't start.. So Im wondering if something else has happened while trying to start the car with the mixture settings way off.

Elombard · 06-14-2006, 04:56 PM

I dont think it will affect start that much the cold start valve and Aux air valve probably takes care of all that? It wont run well but should spit and try to start... Souk is the master.

MotoSook · 06-14-2006, 07:13 PM

If you prime the engine (with the air filter removed, lift the airplate up for a 1-2 second count) then crank it, will it fire? It might die after a bit, but you 'll know it's a fuel problem and not anything else.

What was happening before you adjusted the mixture screw?

MotoSook · 06-14-2006, 07:16 PM

Quote:

Originally posted by Elombard
Souk is the master.

A co-worker friend and I were talking about Beta testing today...somehow it turned into him (jokingly) being the only Beta tester..the man, the king of beta testers...the master...

the..."master beta"

Sorry, but the timing made me grin. Thanks for the compliment Erik, but I'm no more a master than some of you guys...just sharing some of the useless crap in my head

Macel · 06-15-2006, 03:25 AM

Quote:

Originally posted by Souk
If you prime the engine (with the air filter removed, lift the airplate up for a 1-2 second count) then crank it, will it fire? It might die after a bit, but you 'll know it's a fuel problem and not anything else.

What was happening before you adjusted the mixture screw?

The engine RPMs were varying a bit at idle I guess.. It'd rev up a bit then back off.

MotoSook · 08:51 AM

You had a lean or rich hunting which could have been adjusted using the method I described in the adjustment thread. Since it's now warmer out, I will guess that your hunting idle was due to a rich condition. The rich condition was not as noticable during the cooler months since the air was a little thicker. Now when the air temp is 80+ it's a little different story. Add to that the AAR and WUR are reacting differently.

I'm guessing you guys don't have a gas analyzer, which is the other way to do it, but the "field adjustment" method should have worked, if it have been done right.

What you need to do now is get the idle mixture close to what you had, then perform the fine tune adjustment using the field method of idle mixture adjustment. To get it close to what you have, you will have to be patient.

Start with the screw on the lean side of the mark (per your picture, turn it counter-clockwise until you see the screw is pass what looks to be the old position.)

Keep in mind that your car will likely be in the cold start routine still (depends on your ambient temp too). When I say routine, I mean that the warm up regulator (WUR) will still be in the cold stage and allowing a richer mixture once the engine is running. So do not adjust the mixture until the engine is warmed up. That is if your trial and error gets it to idle.

Since you are repeatedly squirting gas into the airbox during the trial and error process to an acceptable idle, you may start to smell gas.

If you start the process on the lean side, the car might fire, then stall after a few seconds. That's promising. Turn the idle mixture screw a 1/4 turn clock wise (to richen) and try again. I'm assuming that you have not touched the air bypass screw on the throttle body. If you have you will have to balance the air and fuel during this trial and error process.

The goal here is to get you to a mixture that will allow the car to idle, even if it's rough. Once the engine will stay running on it's own, you will then make fine adjsutments using the "field method."

If your idle speed is too high, because you tried to adjust the air bypass screw, you will have to bring the idle down in small steps while performing the field method.

tsuter · 06-15-2006, 10:07 AM

I hope you got a pop valve. I smell a nice intake backfire coming with all this blind fiddling and cranking of the motor!!!

Macel · 06-15-2006, 11:20 AM

Quote:

Originally posted by tsuter
I hope you got a pop valve. I smell a nice intake backfire coming with all this blind fiddling and cranking of the motor!!!

Yeah we do.. Actually, we had a couple spectacular backfires while working on it before we really screwed up the mixture. Nothing like a pillar of flame shooting up at your face with a loud "BANG" to wake you up.

Macel · 06-15-2006, 04:28 PM

Well, I got it to fire. It stalls right away, but better than nothing anyway.

If it fires, but stalls right away, is that a guarantee that it is too lean? Or could a too-rich mix do that too?

MotoSook · 05:01 PM

Which direction were you adjusting the mixture screw? Did you continue to turn it and restart like I posted above?

Macel · 06-15-2006, 04:49 PM

Got it running!.. It's literally billowing white smoke out the tailpipe.. Still way to lean I take it?

Well, I was having no luck with the screw where it was.. Car wasn't firing at all.. so I turned it all the way back to lean (ccw) and worked from there.. I got it to fire in lean, but it stalled. Kept adjusting it richer (clockwise) 1/4 to 1/2 a turn like you said and eventually it stayed running.

MotoSook · 06-15-2006, 04:59 PM

Good! Now perform the field idle mixture adjustment...

arcsine · 06-18-2006, 07:14 PM

Quote:

Originally posted by Paulporsche
Do a search on The Push Pull Method of checking your mixture setting without a meter.

Also, as a rule of thumb, provided all components are in good working order:

If the idle oscilates, your mixture is probably too rich.

If you get backfiring through the intake, your mixture is probably too lean.

If, when approaching a stop, the engine momentarilly drops its revs and wants to stall, it's too rich.

If the engine feels choked off and doesn't rev freely to redline: too rich.

If you get a little burbling sound from the exhaust on overrun: probably just slightly too rich.

I have to thank Paul for putting all these symptoms & diagnosese in one place. I have been chasing an extremely high idle (fixed with new AAV/Decel valve) and then an engine wanting to die coming off the throttle coupled with an oscillating idle. Long story short, from three separate adjustments, I have taken almost a quater of turn out of the mixture and the car runs great; rock steady idle, no under run off throtle, pulls hard and immediately throught the rev range, no backfires. My guess is the mixture had been set with the AAV wide open and once those issues were fixed, it became very rich. As soon as I can get access to a CO meter I'll check it but for now I have no indication of a lean condition. Bet this will help my current crap gas mileage to boot.

So thanks Paul

Paulporsche · 06-18-2006, 07:28 PM

I'm glad that worked out for you.

azasadny · azasadny's Garage

Quote:

Originally posted by Paulporsche
Do a search on The Push Pull Method of checking your mixture setting without a meter.

Also, as a rule of thumb, provided all components are in good working order:

If the idle oscilates, your mixture is probably too rich. YES

If you get backfiring through the intake, your mixture is probably too lean. NO

If, when approaching a stop, the engine momentarilly drops its revs and wants to stall, it's too rich. YES

If the engine feels choked off and doesn't rev freely to redline: too rich. YES

If you get a little burbling sound from the exhaust on overrun: probably just slightly too rich. YES

I guess I'll have to adjust my mixture this week and note the baseline and the changes I've made. The car started easily and ran great when I drove it back from Tab Tanner's shop on Friday, but since then, it idles too slow and stalls constantly. I get a "stumbling" upon acceleration and at higher than 3000 rpms.