Adjusting Mixture - No Effect...Help

PorschePilot · 06-01-2005, 08:14 PM

I just finished rebuilding my 2.7 and have it up and running. Driving the car and the engine seems fine, but it idles high and the idle screw has no effect, so I have tried adjusting the mixture by trying to lean the mixture. It idles at 1100 and I can't get it lower.

Questions: The mixture screw was very difficult to turn, is that normal? I turned it 1 turn counter clockwise, to lean it and it didn't have any affect, is 1 turn a lot? I was trying to get it to idle rough and then richen it up a bit, but after 1 turn towards lean I didn't get the idle to slow down or run rough. What am I doing wrong.

MotoSook · 06-01-2005, 08:17 PM

Did you do anything to the CIS during the rebuild?

Do you have any air leaks? Did you do the above with the car hot? Did you change the air screw during the rebuild?

PorschePilot · 06-01-2005, 09:07 PM

I just unbolted the inducton system and cleaned it up and olted it back on. I replaced all the injectors.

I made sure the engine was at operating temp before I attempted any adjustments.

MotoSook · 06-01-2005, 09:13 PM

I have a feeling something is not connected right.

stlrj · 06-01-2005, 09:20 PM

Maybe a vacuum line did not get connected.

Paulporsche · 06-02-2005, 03:13 AM

Pilot,

Often leaning the mixture will raise the revs @ idle. Search the "Push Pull Method" of adjusting the CIS. Try that or try richening the mix for starters. One full turn is a lot; probably at least 8%. Make sure the engine is warm as the AAR may be trying to keep your revs up. Check for air leaks, especially the decel valve.

johnco · 06-02-2005, 03:32 AM

I had the same problem once. you might check the height of the sensor plate. the clip that holds it in place was off, the plate was a little high and I could not lower idle no matter what I tried. once at the proper position, everything was okay

echrisconnor · echrisconnor's Garage

It sounds like you're battling at least two different problems:

1. Idle adjustment
2. Mixture adjustment

Treat them differently for starters. If your idle is high, and the bypass screw has no effect, then you've likely got an air leak. Or, possibly your throttle linkage does not return all the way after re-installing the engine in the car (check to see that all the springs are hooked up). There are a bunch of tests for air leaks in the AAR and AAV or decel valve, If you do a search you can find out about them, but these are likely your prime suspects. However, if you plug the line going to the Decel valve and the pinch off the soft rubber hose which goes out to the AAR and AAV, you can see if they are leaking. All any of these devices do is allow additional air to bypass the throttle plate and raise the revs during certain conditions.

On the mixture front, a leak can throw off your mixture. As has been said though, a full turn of the screw is a big adjustment. Only adjust your mixture after the engine is good and warm and you know you don't have any leaks, the timing is on and the idle is set. There is another method which I've used successfully which is to hook up a vacuum gauge and adjust the mixture up and down until you get the highest point of vacuum reading, then lean it just a hair.