I fooled around with the mixture control unit on my 77 911 3.0 Euro (regular K-Jetronic System) and now it is way out of whack. Any idea's on how I get it back to a somewhat normal mix. Would this be something easy for a real Porsche mechanic with the right tools.

Thanks in advance. <img src="graemlins/crying.gif" border="0" alt="[crying]" /> <img src="graemlins/crying.gif" border="0" alt="[crying]" /> <img src="graemlins/crying.gif" border="0" alt="[crying]" />

 

As I recall, the total breadth of adjustment is a little less than 180 degrees. Set it roughly to the middle and then off to someone who can measure the exhast, and then fine tune the setting. You probably know when you adjust the mixture control, the engine should be off, so you don't damage the fuel distributor itself.

 

OH NO!

Bill, This is the first I have heard that adjusting the idle mixture with the motor running can damage the fuel dist. Can you elaborate please.

 

Hi Bill, when you say the middle, do you mean I should turn the screw all the way cw and then count the # of turns it takes to go CCW then divide by two and turn back CW to get to the middle or by actually viewing the screw in the middle by some other way. Also, do you know if the screw will eventually stop where it can not be turned any further if I was to turn it either CW or CCW or will the screw eventually end and come out of where it is screwed into? For example, the idle adjusting screw, if you continue to turn CCW it will eventually pop out completely to where it was screwed into.
Thanks Bill. I will take to mechanic for fine tuning, once I can get out of garage.

 

If I remember correctly, turn it all the way to the left, then roughly 180 degrees to the right covers the whole range.

 

[quote]<strong>adjusting the idle mixture with the motor running can damage the fuel dist. Can you elaborate please.</strong><hr></blockquote>

Sorry I'm short of time and can't scan a picture in. Let me try with words. On a CIS engine, the mixture adjustment screw sits on top of the arm that, on one side, holds the round metal plate over the air intake and on the other side dips deep into the bowels of the fuel distributor. Remember as air is needed by the system, it flows past the plate, raising it which in turn tells the fuel distributor what to do. If the engine is running, the plate is trying to go up to let air in. If, in addition, the 3mm? hex rod is stuck in the fixture to adjust the mixture, as the arm tries to go up, it can't, and as I recall you can end up bending the arm that attaches to the plate. You may have to do something like try to rev the engine to bend anything. However, I always make the adjustment, pull the hex rod out, then start the engine. Further adjustments, turn the engine off, tune, repeat. I found the CIS engine, once tuned, stays that way for quite awhile.

As an aside, it's alot easier if you have an 80-83 with a lambda system as you can hook up a dwell or duty cycle gauge to read the frequency valve and know if you're running rich or lean, even watch it in operation. There's a connector in the engine compartment to hook into, under the fuel filter. Green/white wire is the signal wire.

 

Thanks Bill. I see the potential for damage.

 

Hi Bill, I tried what I believe you meant above. I turned the mixture control screw all the way counter clockwise until it stopped and then turned 180 degrees clockwise. The plate seemed to resting right where the cone meets the cylinder, so I pushed up on the spring a bit to give it a bit of clearance. I had lent my CIS book out so I was not sure if the plate should be able to fit inside the cylinder and be centered properly so it is not making any contactwith the cylinder walls or if is not suppose to rest within the cylinder. Well I started the car up, ran up to 2000 and immediatley died. When the car died the plate came down and got stuck within the cylinder. I had to push up on to free. My question would be, should the plate be perfectly centered so it can fit down inside the cylinder or should it rest in the cone centered just above the cylinder. Question # 2, could the place where the adjusting screw is suppose to be, be in the middle number of turns it would take to go total from totally ccw to totally cw and then turn 180 degrees cw.
Last, when I took the rubber boot off to see what was going on inside, I noticed everything was covered in oil, the cylinder, the plate, the throttle body. I have cleaned them out since. Would this help explain why it has always runs poorly cold? I believe the oil got in there from when I first purchased the car, I put to much oil in the tank, the excess came out the oil breathing hose into the airbox (alot). I cleaned the airbox but never went any further as far as cleaning. I know this is alot of questions, any help appreciated. Thanks for all your help.

 

One other question, with all that oil sprayed throughout the throttle body, the rubber boot and the air plate, should I remove clean any further than just what is exposed when the boot is taken off.

Thanks.